Unsuspected cocaine exposure in young children. OBJECTIVE: To determine the prevalence of cocaine exposure among preschool children with clinically unsuspected signs and/or symptoms. DESIGN: Prevalence study. SETTING: Pediatric emergency department in an inner-city hospital. PARTICIPANTS: 250 children aged 2 weeks to 5 years who underwent urine assays for cocaine prior to discharge from the emergency department. INTERVENTIONS: None. MEASUREMENTS/MAIN RESULTS: Six (2.4%) of the 250 urine assays (95% confidence interval, 0.5% to 4.3%) were positive for benzoylecgonine, the major urinary cocaine metabolite. Four of the positive urine assays were from children younger than 1 year and all children with positive urine assays were younger than 24 months. None of these children presented with a complaint or was identified as having clinical problems currently associated with childhood exposure to cocaine. Possible exposure routes include breastfeeding, intentional administration, accidental ingestion of cocaine or cocaine-contaminated household dust via normal hand-to-mouth activity, and passive inhalation of "crack" vapors. CONCLUSION: Among the inner-city children served by this hospital, significant numbers of infants and young children are being exposed to cocaine, and this exposure occurs in a clinically unsuspected population. 