This study was undertaken to establish reference values for the size of the uterus and ovaries in newborns. We also studied the frequency and follow-up of functional ovarian cysts in healthy neonatal girls.,P, elvic ultrasonography was performed on 55 normal newborns. Right and left ovarian volumes positively correlated with birth weight and length, but there was no correlation between uterine length and any of the parameters studied. In a total of 55 newborns, 16 ovarian cysts were detected by transabdominal ultrasound: six neonates (10.9%) had cysts on the left side, ten (18.2%) on the right side, and two (3.6%) had bilateral cysts. All were uncomplicated homogeneous cysts and resolved spontaneously. A higher percentage of cysts was found in the 26 infants weighing 2,5002,999 g, ten (38.4%) of whom had cysts, than in the 29 infants weighing 3,000 g or more, four (13.7%) of whom had cysts (p < 0.05). Newborns with cysts were followed up, and the cysts resolved spontaneously within 3 months in all but three patients in whom resolution took almost 6 months. Right and left ovarian volumes were positively correlated with birth weight and length, but no significant correlation was found between uterine length and any parameter. In conclusion, ovarian volume was found to be reduced in newborns with relatively low birth weight s well as intra-uterine growth retardation. Functional cysts were more prevalent among low birth weight girls. We suggest that small ovaries and ovarian dysfunction may have a prenatal origin, and further studies on normal and growth-retarded newborns are needed.