Globally, mastitis is an important production disease in the dairy industry and has a great economic impact due to reduced milk yield, milk quality deterioration, treatment costs, culling, risk for antimicrobial resistance and reduced animal welfare. A cohort study was conducted on 24 randomly selected dairy farms in Chittagong during six months to (1) estimate the incidence of clinical mastitis (CM) at cow level, (2) identify risk factors and (3) isolate causative pathogens. CM was defined as grade-I (changes in milk), grade-II (changes in milk and udder) and grade-III (changes in milk and udder along with systemic changes).