Although renal calculi and cyst calcifications occur commonly in patients with autosomal dominant polycystic kidney disease (ADPKD), their true frequency is unknown because it is difficult to distinguish between the two with excretory urography and sonography. A detailed analysis of renal calcifications in ADPKD based on CT findings has not been performed. Accordingly, we retrospectively evaluated clinical and CT findings in 84 patients with ADPKD to determine the frequency of calculi and cyst calcifications, the relationship of these abnormalities to symptoms, and possible factors in their pathogenesis. Of the 84 patients, 53 had both IV contrast-enhanced and unenhanced CT scans and 31 had unenhanced scans only. We examined unenhanced CT scans of all 84 patients for renal calcifications. However, we classified renal calcifications into stones and cyst calcifications in only the 53 patients, because it is often difficult to distinguish between the two when only unenhanced scans are available. Of 84 patients, 18 (21%) had passed renal calculi or had stones treated surgically and 42 (50%) had renal calcifications on CT. Of the 53 patients who had both enhanced and unenhanced CT scans, 19 (36%) had renal calculi on CT. Patients with stones had significantly higher frequencies of previous flank pain (68% vs 35%) and of urinary tract infections (63% vs 18%) than did those without calculi. Cyst calcifications occurred in 13 (25%) of 53 patients and were probably a consequence of cyst hemorrhage. Cyst calcifications were found significantly more often in older patients with larger kidneys and worse renal function. We conclude that renal stones have a high rate of occurrence among patients with ADPKD and are a significant cause of morbidity in this disorder. Cyst calcification is also common in patients with ADPKD, particularly those with more advanced cystic disease.