To assess the clinical characteristics of bacteremic urinary tract infection (UTI) in children. Clinical data of Finnish children with bacteremic UTI (n = 134) from 1985 to 1994 were analyzed. Their symptoms, laboratory and imaging findings were compared with those of age- and sex-matched patients hospitalized for blood culture negative UTI. Generally, no major differences were seen in clinical findings between bacteremic and nonbacteremic patients. Bacteremic children had more frequent feeding problems (P = 0.02), and children > or =12 months of age tended more often to have abdominal pain and vomiting than did nonbacteremic patients. Fever was the major initial symptom in both study groups, but no significant difference occurred in the mean highest temperature or in the mean of duration of fever before admission to the hospital. The mean concentration of serum C-reactive protein on admission was significantly higher in bacteremic patients (116 vs. 76 mg/l; P < 0.01). After onset of antimicrobial treatment fever lasted significantly longer in bacteremic patients than in control patients (means, 2.3 vs. 1.1 days; P < 0.01). Anatomic or functional abnormalities in the urinary tract were detected in 51% vs. 46%, respectively. Obstruction of the urinary tract (9% vs. 1%, P < 0.01) and Grade 3 to 5 vesicoureteral reflux (30% vs. 16%, P = 0.02) were significantly more frequent in bacteremic patients with UTI. Obstruction or vesicoureteral reflux was found in 46% of children with bacteremic UTI caused by Escherichia coli vs. 89% of children with non-E. coli infection (P < 0.01). Clinical symptoms do not significantly distinguish bacteremic from nonbacteremic children with UTI. Outcome of bacteremic UTI was comparable with that of nonbacteremic UTI. Bacteremic children, especially those with non-E. coli UTI, more often had anatomical or functional abnormalities in the urinary tract.