Background: Nephrologic investigation is recommended in neonates ≥34 wk gestation with spontaneous pneumothorax (PTX) because of a 19% prevalence of major urinary tract anomalies in an autopsy series(Pediatrics 1977; 59: 1048-1049). Objective: To determine the prevalence of major urinary tract anomalies in infants with non-fatal, symptomatic, spontaneous PTX and to determine the associated clinical characteristics. Design: A retrospective study was conducted of neonates with PTX admitted to one institution between January, 1989 and June, 1995, with a gestational age > 34 weeks who lacked known causes of neonatal PTX including respiratory distress syndrome, meconium aspiration syndrome, oligohydramnios sequence, or positive airway pressure. Symptomatic PTX was defined as pulmonary air leak manifest by cyanosis, retractions or tachypnea requiring admission to a neonatal intensive care unit(NICU). Major urinary tract anomalies were defined as hydroureter, hydronephrosis, or dysplastic, polycystic, or multicystic kidneys. Urinary tract anatomy was determined by ultrasonography in 19 infants and at autopsy in 1 infant who died from unrelated gastrointestinal causes at 4 months.Results: Twenty infants fulfilled study criteria. Mean birth weight = 3227 g ± 112 (SEM) and mean gestation age = 38 wk ± 0.4. No study infant had major urinary tract anomalies (95% CI: 0 - 0.14). Eighteen infants (90%) were white, which was significantly increased compared to all other infants > 34 wk gestation, 521 (59%), admitted to the NICU during the study period, (P =.005). Sixteen infants (80%) were male, which was not significantly increased compared to the reference group, (P =.24). PTX was documented radiographically at a median of 9 hours of age (range 1 - 72), and 4 infants had bilateral pneumothoraces. Conclusions: 1) Major urinary tract anomalies were not associated with non-fatal symptomatic spontaneous PTX in near-term and full-term neonates; therefore, screening renal ultrasound studies may not be indicated. 2) White ethnicity was significantly associated with symptomatic spontaneous PTX in neonates.