Long term effects of gastrocystoplasty in rats. Twenty prepubescent rats underwent microsurgical gastrocystoplasty by a technique which is described. An equal number of control rats had their bladders opened and closed. Rats were sacrificed at 16 to 18 months postoperatively. There were no differences in final weight, serum electrolytes, or renal function between the two groups. Prominent histopathologic changes of the bladder occurred in the gastrocystoplasty group. These changes included papillomas present in five of the 15 rats surviving long term. No significant changes occurred in the bladders of the control group of rats. Possible etiologies and the significance of the rats. Possible etiologies and the significance of the gastrocystoplasty related lesions are discussed. 