Peculiar ring-like structures identified as Liesegang rings (LRs) were found in renal cyst fluid from three patients with benign renal cysts. They ranged in size from 5 to 820 mu. Most had a double-layer outer wall with equally spaced radial cross-striations and an amorphous central nidus. Special stains were performed in one case, and the results are discussed. Reports of LRs in cystic or inflamed tissues have recently appeared in the literature. Some LRs have been mistaken for eggs or mature components of the giant kidney worm, Dioctophyma renale. We propose that cytologic assessment of renal cyst fluid in conjunction with histologic examination decreases the likelihood of misdiagnosis of LRs.