Fifty-four ill or nonproductive lemmings (Dicrostonyx spp.) were evaluated for signs, lesions and causes of disease for 5 yr in a domestic colony. Parasitic granulomas caused by Encephalitozoon cuniculi were the most common finding and were seen in 22 lemmings. The disease was characterized by circling and torticollis with granulomas in many tissues, especially the central nervous system. Suppurative otitis occurred in 12 lemmings and was associated with Klebsiella pneumonia infection; circling was the common sign. Hepatic microabscesses were present in seven lemmings but a cause was not identified. Five lemmings had neoplasms and 14 had either suppurative processes, aspermia, or ovarian cysts.