Our objective was to determine maternal characteristics and perinatal outcome of unplanned unattended deliveries en route to the hospital in comparison to unplanned deliveries attended by medical personnel within the parking facility of the hospital. All singleton deliveries occurring between 1988 and 1999 were analyzed from the computerized perinatal database. Maternal characteristics and pregnancy outcome of unattended, unplanned out-of-hospital births were compared with unplanned deliveries in the hospital parking lot, with the assistance of medical personnel. Out of 2328 out-of-hospital deliveries, 5.7% ( n=133) were managed by medical personnel in the parking lot and 94.3% ( n=2195) occurred en route to the hospital. The birth weight of newborns from the attended out-of-hospital delivery group was significantly higher than the comparison group (3126.2+/-516 g vs. 3019+/-522 g; P=0.023). A significant linear association was found between birth weight and attended out-of-hospital births (Mantel-Haenszel test for linear association; P=0.002). Moreover, these newborns were significantly more likely to be large for gestational age (OR=2.2, 95% CI 1.2-3.9; P=0.004). Parturients who delivered in the parking lot with the assistance of medical personnel, had significantly higher rates of grade 2 perineal tears (OR=8.4, 95% CI 1.1-5.4; P=0.041). Perinatal mortality was non-significantly higher among attended out-of-hospital deliveries (OR=2.8, 95% CI 0.8-8.3; P=0.279) as compared to unattended out-of-hospital deliveries. The attendance of medical personnel in unplanned out-of-hospital deliveries did not influence the birth outcome.