We have described the clinical, radiologic and endoscopic findings in 84 children with bladder diverticula and 9 children with posterolateral pouch-like protrusions of the bladder wall. Cystoscopically, a new bladder diverticulum is described, resembling a walnutshell. The majority of children had symptoms of urinary tract infection, the walnutshell-like diverticula was frequently associated with haematuria. In 66 or 84 children with bladder diverticula and in 9 children with posterolateral pouches no obstruction of the lower urinary tract was found. Diverticula caused by obstruction were found in 18 cases. Vesicoureteral reflux was present in 34 of 66 children with diverticula without obstruction of the lower urinary tract, in 20 of these there were saccules (diverticula smaller than 2 cm in diameter). Vesicoureteral reflux was found in 8 of 9 children with posterolateral pouches of the bladder wall. Long term follow-up suggests that any protrusion of the bladder wall, regardless of the size of cavity and the shape of the opening, may become a diverticulum associated with further abnormalities of the urinary tract. In 3 patients with postero lateral pouches a transformation from pouches into true diverticula together with the development of vesicoureteral reflux was observed.