• We determined the prevalence of cocaine and cannabinoid exposure among young children presenting to an urban pediatric emergency department without signs or symptoms suggestive of the exposure. The study included 460 children between 1 and 60 months of age in whom urinalysis was required for investigation of routine pediatric complaints. Anonymously and without informed consent, an aliquot of urine was screened for cocaine metabolite (benzoylecgonine) and 11- or Δ-9-tetrahydrocannabinol-9 carboxylic acid with the enzyme multiplied immunoassay technique. Positive specimens were rescreened with a radioimmunoassay and confirmed with gas chromatography/mass spectrometry, if a sufficient quantity of urine was available. Benzoylecgonine was identified in 25 patients (5.4%) by both screening techniques. Enough urine was available for confirmatory testing in eight patients, and all eight urine specimens contained benzoylecgonine. Neither 11- nor Δ-9-tetrahydrocannabinol-9 carboxylic acid was detected in any patient. We documented the magnitude of the problem of occult passive cocaine exposure in young children living in an urban environment. Such exposure has serious implications for the assessment of outcomes in postnatal follow-up studies of prenatally exposed children as well as potential risks to children living in household environments where occult cocaine exposure occurs.