Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent of the hereditary diseases affecting the kidney but it can also be associated with cysts in the pancreas, liver, arachnoid, seminal vesicles. In particular, ADPKD plus adult polycystic liver disease (APLD) is defined as Potter type III. In the literature, the association of malignant neoplasm with APLD and ADPKD is extremely rare. We have found only nine cases. Only one report described multiple gastric carcinomas associated with Potter type III cystic disease. We described a case of a man suffering from ADPKD and APLD plus a stage IV (TNM) gastric adenocarcinoma.