Order unanimously reversed and new trial granted. Memorandum: Family Court's determination of paternity was contrary to the weight of evidence. Complainant's testimony was vague and contradictory and the proof fell short of the legal requirement that paternity be established by evidence which is "clear, convincing and entirely satisfactory" (Matter of Piccola v Hibbard, 51 A.D.2d 674, affd 40 N.Y.2d 1035). The complaining witness gave birth to a daughter weighing 3 pounds, 10 ounces on July 16, 1974. It was complainant's uncorroborated testimony that the child was conceived as the result of a single act of intercourse occurring either in October or November of 1973 but she was unable to determine which month. The date was never established to the satisfaction of the trial court and it was particularly important in determining credibility because of the infant's low birth weight which made either time of conception questionable. Under the circumstances, medical testimony was required to support the credibility of complainant's story (see Matter of Morris v Terry K., 60 A.D.2d 728; Matter of Kathy R. v Steven S., 47 A.D.2d 680; Baranowski v Luciano, 23 A.D.2d 815).