Ectopic pregnancy (EP) is becoming a more and more frequent problem in many developed countries, but the cause of such increase is not fully understood. Improved diagnosis certainly explains part of it, but also the changing lifestyle and sexual habits might play an important role. During the years 1990-1993, 56 women were admitted into the Divisione di Ostetricia e Ginecologia of the Istituto per l'Infanzia of Trieste because of EP diagnosed on the basis of clinical history and signs, transvaginal echography and serum HCG levels. 33 of them underwent surgical operation for the presence of severe abdominal pain, hemoperitoneum greater than 50 cc, and increases HCG level. The other 23 women were treated conservatively. Taking into account the approximate date of conception both for ectopic and other pregnancies, the monthly incidence of EP was computed and showed a statistically significant peak during the summer period (14.4%) compared to the other periods (6%). The increased frequency of EP among pregnancies started during the warmer months is interesting not only as a descriptive result, but also because it may contribute to a better understanding of the conditions under which the ectopic development of the fertilized ovum may take place.