In Westerhof v Gee Estate, the Ontario Court of Appeal decided that participant experts and non-party experts may give opinion evidence without complying with Rule 53.03. In other words, a fact witness who is considered an expert may give opinion evidence without filing an expert report or fulfilling any of the other requirements normally applicable to litigation experts. The decision narrows the scope and application of the rules on experts who are engaged by a party to provide evidence including the requirement to file an expert report.

The decision arises from two cases involving motor vehicle accidents. The question on appeal was whether and to what extent medical witnesses could give opinion evidence at trial. In the one case, the trial judge ruled that medical witnesses, who had treated the plaintiff but did not comply with Rule 53.03, could not give opinion evidence concerning diagnosis or prognosis, even if they had not been retained for the purpose of the litigation. This decision was overturned. In the second case, the trial judge permitted the treating physicians to give opinion evidence concerning matters such as the future employability and future medication requirements of the plaintiff. This decision was upheld.

The Court has created two categories of experts:   litigation experts and participant experts or non-party experts. Rule 53.03 applies to “litigation experts” – i.e., those experts retained by counsel. But the rule does not apply to “participant experts”, who prior to the 2010 amendments to Rule 53 were considered to be fact witnesses. An example of a participant expert is a treating physician who is permitted to testify about opinions that arise directly from her treatment of her patient. Participant experts are not covered by Rule 53 because they are not “engaged by or on behalf of a party to provide evidence in relation to a proceeding.”

Justice Simmons lays out the following test on when a witness may give opinion evidence:

A witness with special skill, knowledge, training or experience who has not been engaged by or on behalf of a party to the litigation, may give opinion evidence for the truth of its contents without complying with rule 53.03 where:

    • the opinion to be given is based on the witness’ observations of or participation in the events at issue; and
    • the witness formed the opinion to be given as part of the ordinary course of his or her skill, knowledge, training and experience while observing or participating in such activities.

The Court goes further to state that Rule 53.03 does not apply to the opinion evidence of a non-party expert where the non-party expert has formed a relevant opinion based on personal observations or examinations relating to the subject matter of the litigation for a purpose other than the litigation. However, the Court has put a limit on this testimony. If the participant expert or non-party expert’s opinion goes beyond the scope of an opinion formed in the course of observation, the Court could require the witness to comply with Rule 53.03.

The Court was not persuaded by disclosure problems  in relation to the opinions of participant experts and non-party experts. The Court reasoned that in many circumstances, these experts will have prepared documents summarizing their opinion about the matter contemporaneously with their involvement. If they have not, then it is open to the party as part of the discovery process to seek disclosure of any opinions, notes or records of participant experts and non-party experts that the opposing party intends to rely upon. The Court’s reasoning on this point may have been influenced by  the fact that many of the participant experts who were excluded from testifying in this case were physicians who must have had contemporaneous notes. But that will not always be the case.

The Court also relies on public policy reasons to justify its decision. “Requiring participant witnesses and non-party experts to comply Rule 53.03 can only add to the cost of the litigation, create the possibility of delay and add unnecessarily to the workload of persons not expecting to have to write Rule 53.03 compliant reports.”

The Court indicates that the trial judge retains a gatekeeper function and may exclude certain evidence. This would especially be the case if the medical practitioners were litigation experts in disguise.

Practice  Points:

  • On discovery, make sure to ask broad questions about any potential opinions of fact witnesses that may exist in the record.
  • At trial, any fact witness who have special skills, knowledge or training, may be asked for his or her opinion. The Court does not address how such witnesses will be qualified as experts. Qualification will most likely need to be established.
  • There is language in the Court of Appeal’s decision that reminds litigators   that judges do not like “hired guns” and may therefore find the opinion of fact witnesses and non-party experts to be persuasive.


Ewa Krajewska


Litigation and Arbitration
Insurance and Tort Liability
Appellate Advocacy