Congenital solitary functioning kidney (CSFK) is a relatively common renal malformation and in children is frequently complicated by anomalies of the ipsilateral genital organs and occasionally by anomalies of other organs. The aim of this study was to determine the incidence of associated urological, cardiac, gastrointestinal, hematological, neurological, skeletal, and other congenital malformations in children with CSFK. We retrospectively reviewed 87 consecutive cases of CSFK diagnosed at our hospital between 1995 and 2003. There were 45 boys and 42 girls, whose ages at diagnosis ranged from newborn to 16 years (mean 4.67 +/- 4.48 years). In all patients, CSFK was diagnosed by abdominal ultrasound and confirmed by radionuclide studies. In 46 patients (53%) the left kidney was absent, and in 41 patients (47%) the right kidney was absent. Overall associated anomalies were detected in 52 of the 87 children (60%) with CSFK. Urological anomalies were most common, with an incidence of 37% (32/87). Nonurological anomalies were detected in 38 children (44%) with CSFK; these included cardiac anomalies in 13, gastrointestinal anomalies in eight, hematological anomalies in five, neurological anomalies in three, and other organ anomalies in nine. In our study, more than half of the patients with CSFK had associated anomalies. For this reason we recommend abdominal ultrasound and voiding cystourethrogram for early recognition of urological anomalies and a careful physical examination for other organ anomalies in patients with CSFK.