Unless the court orders otherwise, questions calling for the opinion of an expert witness need not be hypothetical in form, and the witness may state his opinion and reasons without first specifying the data upon which it is based. Upon cross-examination, he may be required to specify the data and other criteria supporting the opinion.
R 4515.Form of expert opinion
Article 45. Evidence · Last amended 1963 · Last verified July 21, 2026
In one sentenceCPLR 4515 frees an expert witness from the old hypothetical-question format, letting the expert state an opinion and reasons directly, while preserving the cross-examiner's right to probe the underlying data.
Full Text of CPLR 4515
Plain-English Summary
CPLR 4515 modernizes how expert testimony comes in. Unless the court orders otherwise, a lawyer questioning an expert does not have to build an elaborate hypothetical question that recites every assumed fact before asking for an opinion. The expert can state the opinion and the reasons behind it without first laying out the data on direct examination.
Cross-examination keeps the check on this shortcut: the opposing party can require the expert to specify the data and other criteria that support the opinion. That preserves the ability to test and challenge the basis for the opinion, even though the direct examination is no longer bound to the old, cumbersome format.
Frequently Asked Questions
Does an expert witness have to answer a hypothetical question in New York?
No, not unless the court orders otherwise. CPLR 4515 lets an expert state an opinion and reasons without the question being framed as a hypothetical.
Does an expert have to explain the data behind an opinion before giving it?
Not on direct examination. CPLR 4515 lets the expert state the opinion and reasons first; the data can be drawn out on cross-examination instead.
Can opposing counsel demand to know what data an expert relied on?
Yes. CPLR 4515 lets the cross-examiner require the expert to specify the data and other criteria supporting the opinion.
Can a court require the old hypothetical-question format for expert testimony?
Yes. CPLR 4515 gives the court discretion to order that format if it chooses, though the section's default dispenses with it.
What problem was CPLR 4515 designed to fix?
It curbed the abuse of long, convoluted hypothetical questions that made expert testimony harder to follow while still letting cross-examination test the opinion's basis.
Advisory Committee Notes
This rule is new. It is based upon § 9 of the Model Expert Testimony Act and rule 58 of the Uniform Rules. It is designed to provide the trial judge with the discretion necessary to obtain the maximum benefits from the use of witnesses by limiting the abuse of hypothetical questions. It will permit the expert to state what he knows in a natural way; at the same time, it gives the cross-examiner full opportunity to discredit him. The rule is consistent with the major efforts by the medical and legal professions to cooperate in the administration of justice. See Margett, Standards of Practice for Doctors and Lawyers, 29 NYS Bar Bull 187 (1957).
Amendment History
Add, L 1962, ch 308; amd, L 1963, ch 808, § 1, eff Sept 1, 1963.
Source & verification. Provision text, History, and Advisory
Committee Notes are reproduced verbatim from the Consolidated Laws of New York.
Last verified July 21, 2026.
· Official source
Also known as: expert witness opinion form New Yorkhypothetical question expert testimony CPLRexpert witness cross examination data New York