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.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.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).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.