In order to investigate urinary bacteriology in relation to calculus formation in continent urinary reservoirs, a retrospective study was conducted of 19 patients with the Kock pouch and 23 patients with the Indiana pouch. Analysis of a total of 151 urine cultures showed that asymptomatic bacteria (any bacterial count) were present in 92% of urines from the Kock pouch and 74% from the Indiana pouch. The incidence of organisms and total bacterial counts were similar for both pouches. The most prevalent organisms were Escherichia coli, Pseudomonas sp., Klebsiella sp., Proteus sp., Enterobacter sp., and Enterococcus sp. Urinary calculi developed in 42% of the Kock pouch patients and 13% of the Indiana pouch patients. More than half of the patients had multiple stone recurrence. Infectious stones developed in 32% of the Kock pouch patients, usually on the foreign materials, and 9% of the Indiana pouch patients. In general, no clear relationship was established between urinary bacteriology and calculus formation although Proteus sp. or Providencia sp. was determined to be the causative organism in some infectious stones. Furthermore, metabolic stones developed in 32% of the Kock pouch patients and 9% of the Indiana pouch patients. Because calcium phosphate was a constituent of 80% of the metabolic stones, the presence of urinary factors promoting calculus formation was suspected.