Fecal samples from diarrheal patients and non-diarrheal controls were examined for Cryptosporidium oocysts in a year-long prospective study at a diarrhea treatment center in Dhaka, Bangladesh. Cryptosporidium oocysts were detected in 42 (3%) of 1,382 diarrheal patients but in none of 235 non-diarrheal controls. In 32 (76%) of 42 patients, no other enteropathogens were detected. Children <5 years of age were more commonly infected than older children (4.8% vs. 1.6%, P > 0.05) and adults (4.8% vs. 0.2%, P < 0.01). A higher number of cases were detected during hot and humid months (April–July). Nineteen children <5 years of age (index cases) and their 71 family members were followed for 3 weeks after the release of the index cases from the hospital. Diarrhea continued for >14 days (persistent diarrhea) in 8 (32%) index children. Cryptosporidium oocysts were detected in 1 (12.5%) of 8 family members who developed diarrhea during the follow-up period. Index cases excreted oocysts for 3–28 days (12.37 ± 8.35 days). Almost all the patients recovered with oral rehydration. Cryptosporidium ssp. cause self-limited diarrhea episodes in children <5 years of age in Bangladesh, with a low frequency of intrafamilial transmission.