The giant congenital vesical diverticulum of the bladder is very uncommon; three observations are described. The clinic symptomatology is ruled by acute retention of urine and by dysuria. The I.V.P. always shows the important reverberation on the renal cavities. In two cases the diagnosis has been done thanks to the cystography. Concerning the third child both clinic and paraclinic symptoms inclined to favour the diagnosis of an abdominal cystic hygroma but the surgical procedure showed it was a bilateral vesical diverticulum. The surgical treatment is made up of endo and latero-vesical diverticulectomy with reimplantation of the homolateral ureter which is always implanted in the posterior pouch. With its clinical, anatomical and physiopathological aspects, the giant congenital diverticulum of the bladder must be differentiated with the little diverticulum.