This study investigates the influence of the new and full moon on onset of labor and spontaneous rupture of membranes. Admissions during the year 1984 to the labor and delivery unit of a large urban hospital in Cleveland, Ohio, in spontaneous labor or with rupture of the membranes, comprised the sample population (N = 1999). Barometric pressure for each day of 1984 and the days of the full and new moon were also recorded. Frequencies for onset of labor and spontaneous rupture of membranes at the full and new moon were compared with days controlled for barometric pressure. Contingency analysis by chi-square was used. Results show a positive significant correlation of the onset of labor to the full moon when barometric pressure is not controlled. Frequencies of onset of labor and spontaneous rupture of membranes show positive nonsignificant correlation when barometric pressure is controlled. Results indicate a compounding, if not primary, influence by barometric pressure to that of the full and/or new moon.