Objectives: To investigate the obstetric antecedents for preterm delivery (PTD) in an Irish urban obstetric population, and to evaluate the incidence and outcome of such deliveries.Study design: A retrospective observational study of all preterm deliveries at the Rotunda Hospital, Dublin during the six-year period 1997-2002. The findings for early preterm deliveries (EPTD) (24 + 0-31 + 6 weeks' gestation), and late preterm deliveries (LPTD) (32 + 0-36 + 6 weeks' gestation) were analyzed separately.Results: There were 38,795 deliveries after 24 weeks' gestation or) 500 g birth weight, of which 2839 (7.3%) were preterm. Of all preterm deliveries, 626 (22.1%) were EPTD and 2213 (77.9%) were LPTD, resulting in an EPTD rate of 1.6% and an LPTD rate of 5.7%. Spontaneous unexplained preterm delivery accounted for 1221 (43.0%) of preterm deliveries (PTD), and of these 213 (34%) cases were EPTD and 1008 (45.5%) LPTD. The other most frequently observed obstetric causative factors, in order of importance, were multiple gestation (676; 23.8% of PTD), hypertensive disorders of pregnancy (243; 8.6%), antepartum hemorrhage (194; 6.8%), stillbirth (105; 3.7%), intrauterine growth restriction (53; 1.9%) and preterm prelabor rupture of membranes +/- chorioamnionitis (32; 1.1%). There were 75 early neonatal deaths among infants born prematurely, plus 105 stillbirths, resulting in a perinatal mortality rate of 63 per 1000 for PTD (n = 180), which on subsequent analysis was 158 per 1000 for EPTD (n = 99) and 37 per 1000 for LPTD (n = 81).Conclusions: These data outline the obstetric factors linked to preterm delivery within a recent Irish urban obstetric population. Spontaneous idiopathic preterm labor was the principle causative factor in 43% of all preterm deliveries, and represents the proportion of women for whom future therapeutic intervention may be of benefit.