A longitudinal prospective study design was conducted from February 2021 to September 2021 on calf diarrhea and cryptosporidiosis in urban and peri urban areas of Bahir Dar, Northwest Ethiopia. The specific objectives were: to quantify the incidence of calf diarrhea and cryptosporidiosis in bovine calves and also examining the association between calf diarrhea and cryptosporidiosis in bovine calves. Simple random sampling technique was employed to sample dairy farms, whereas one stage cluster sampling was used to sample dairy calves. Univariable and multivariable Cox proportional hazard regression models were used to estimate the effect of predictor variables on calf diarrhea and cryptosporidiosis from birth to 90 days of calf age. Sheather’s sugar solution flotation techniques followed by Modified Ziehl–Neelsen staining technique was used to identify Cryptosporidium Oocysts. A total of 384 calves were considered for this study. Accordingly, of total calves examined 28.9% calves were diagnosed with diarrhea. Among diarrheic calves 52.25% of calves were diagnosed with cryptosporidiosis. The overall incidences rate of calf diarrhea and cryptosporidiosis found in this study were 41.2 cases per 100 calf three months at risk (risk rate of 33.76%) and 25.2 cases per 100 calf three months at risk (risk rate of 22.2%),respectively. Age of calf (<2months) (HR = 3.41, 95% CI; 2.153 - 7.117; P=0 .000), body condition (HR = 1.60, 95% CI; 0.541-3.685; P=0.000), season (HR = 2.167,95% CI; 1.044-3.716; P<0.022) were found significantly (P < 0.05) associated with diarrhea. Whereas, calf age (<2month) (HR = 5.997, 95% CI;3.190-11.273; P< 0.001), sex of calves (HR = 1.753, 95% CI; 1.121-2.742 P< 0.016), calf body condition (HR=2.358 , 95% CI; 1.08 - 4.48; P<0.026); and season (HR=0.57, 95% CI; 0.338- 0.963; P<0.036) were found significantly (P < 0.05) associated with cryptosporidiosis. Besides, this study revealed that the association between calf diarrhea and cryptosporidiosis was statistically significant (X 2 =125.35, P<0.001). Environmental hygiene, nutrition and health care can help to reduce the incidence of calf diarrhea and cryptosporidiosis in the study area. Moreover, the high prevalence of cryptosporidiosis in the study area might pose a significant public health concern which necessitates further in-depth investigation.