We determined the prevalence of cocaine and opiate exposure and the association of exposure with objective physical findings in children presenting to an urban pediatric emergency department. The study included 942 children between one and 60 months of age who required urinalysis for investigation of their chief complaint. Anonymously and without informed consent, urine was screened for benzoylecgonine (BE) and opiates, using an enzyme multiplied immunoassay technique (EMIT) with sensitivity of 50 ng/ml. EMIT-positive samples were rescreened using a fluorescence polarization immunoassay (FPIA). Specimens positive by both EMIT and FPIA were confirmed by gas chromatography/mass spectrometry (GC/MS) if sufficient quantity of urine was available. BE was identified in 41 (4.4%) and opiates in 46 (4.9%) patients by both EMIT and FPIA. The presence of BE or opiate was confirmed by GC/MS in all 34 cases where sufficient urine was available. The age- and sex-adjusted systolic and diastolic blood pressure percentiles were greater, and head circumference and weight percentiles were lower in BE-positive patients compared to those with negative drug screens. There were no associations between opiate exposure and any of these variables. We conclude that occult postnatal cocaine exposure is associated with measurable physical and physiologic differences.