A prenatal diagnosis of adult polycystic kidney disease (ADPKD) by DNA testing is reported. Evidence showing a linkage between the disease and the DNA markers on chromosome 16 was obtained in the family by linkage analysis and homogeneity testing with Italian families of the linked type. Prenatal diagnosis was performed either by polymerase chain reaction (PCR) of GGG1 fragment either by Southern blotting analysis of the others chromosome 16 markers. Diagnostic results were available by PCR analysis in a few hours and then were confirmed by Southern blotting of the others probes. The foetus was monitored by ultrasounds. At 26th week the foetal kidney were enlarged with small cysts and, at birth, the newborn had bilateral renal cysts, confirming the foetal genotype prediction based on flanking markers.