An investigation of possible seasonal patterns in ectopic tubal pregnancies was conducted. The computer data utilized were based on all ectopic pregnancies, abortions and deliveries (total pregnancies) recorded in the Department of Obstetrics and Gynecology at the Chaim Sheba Medical Center, Israel, between the years 1986 and 1989. Composite monthly cohorts of ectopic tubal pregnancies and total pregnancies were constructed for each month of the year, and the probability of an ectopic pregnancy was estimated. A statistically significant increase in the probability of conception rate resulted in ectopic pregnancies which occurred during winter and spring, especially in January to June. The probability of ectopic tubal pregnancies was low (0.50%) in September and high (1.81–1.42%) in December to January. When we studied primigravidae, the same seasonal pattern was observed. The findings of our study suggest, for the first time, that there is an association between meteorological and environmental factors, and ectopic pregnancies. These factors should be considered in the epidemiology of ectopic tubal pregnancies.