Cases of foreign bodies in the bladder self-inserted via urethra are not rare in childhood. Urinary tract infection, dysuria, lower abdominal pain, or haematuria with and without pain are common symptoms. We report on a 11-year-old boy with accidentally detected microscopic haematuria, proteinuria and leukocyturia. Because of increasing proteinuria up to 2330 mg/g creatinine and elevated antistreptolysin titre glomerulonephritis was suspected. However, some echogenic material was detected in the bladder by ultrasound. X-ray of the pelvis showed a 30 cm long tube projecting onto the bladder. The boy then admitted having had inserted a plastic tube into the urethra two years ago. The foreign body was removed cystoscopically. Four weeks after cystoscopy erythrocyturia, leucoyturia and proteinuria had disappeared. We state that symptoms of a local inflammation caused by a foreign body in the bladder can imitate the symptoms of nephritis.