We have investigated if biological rhythms, which affect many physiological and pathological events, influence the time of birth. Two hundred and sixty-three cases who were hospitalized with a diagnosis of active labor and who delivered vaginally were enrolled in the study. Information about the age, gravidity, parity, gestational age on admission, and time of onset of labor and birth was registered. A Morningness-Eveningness Questionnaire (MEQ) was administered for determining the patients' chronotypes and dividing them into a morning- or evening-type group. While 20 (35%) of the morning-types delivered between 18:00 and 24:00h, only 11 (19%) of them delivered between 06:00 and 12:00h. From the evening types, 6 (33%) delivered between 18:00 and 24:00h and 3 (17%) between 06:00 and 12:00h. We conclude that there was no statistically significant difference between the chronotypes in terms of delivery time.