We studied the records of 43 patients with significant bacteriuria caused by Corynebacterium group D2. All suffered from underlying diseases, and 54% were immunosuppressed. The predisposing factors were urologic procedures (100%), previous use of antibiotics (90%), age greater than 65 years (65%), and previous urinary tract infections (UTI;60%). Two-thirds of the patients had urinary tract symptoms, and these symptoms were more common in men than in women. The existence of previous lesions in the bladder favored the development of serious urinary symptoms (encrusted cystitis). Alkaline urine had abnormal sediment that yielded Corynebacterium group D2 in the absence of other microorganisms, a result suggesting that this organism could be an etiologic agent of UTI. Because cultures of urine may appear to be sterile, prolonged incubation must be used to detect Corynebacterium group D2. Correct treatment improved the outcome and probably prevented the development of encrusted cystitis in most of our patients.