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To avoid potential contamination, it is recommended that the first few drops of urine be discarded when obtaining a catheterized urine sample from a child being evaluated for a urinary tract infection (UTI). The existing evidence to make such a recommendation is scant. Our goal, therefore, was to determine whether the urinalysis, Gram stain, and culture results were significantly different from the initial and later urine samples collected from catheterized children.A prospective diagnostic discrimination between early and later urine samples was conducted on a convenience sample of pediatric patients being evaluated for a UTI in an urban emergency department. Results of the urinalysis, Gram stain, and quantitative culture were compared between the early and later stream urine samples.Data from 86 children were analyzed. Four of 80 patients had a false identification of low colony count bacteruria from the early but not from the later stream. For patients with negative cultures, the early stream was also more likely to falsely identify ≥ 5 wbc/hpf (P< 0.01) or bacteruria (P< 0.05) on urinalysis than the later stream.There is a small but potentially meaningful contamination of the early stream urine compared with the later stream in young children catheterized to evaluate for a urinary tract infection.