BACKGROUND: Dairy products intolerance is defined by existing of gastrointestinal symptoms following dairy product consumption. Its prevalence varies among different countries. This study is conducted to determine the frequencies and severities of intolerance symptoms in the consumption of different dairy products in Iranian students of Medical Sciences.METHODS: In this cross-sectional study, 1041 students from Isfahan University of Medical Sciences who apparently were healthy and had not used any drug before, participated. The questionnaire included information about dairy product consumption and avoidance, severity of dairy intolerance symptoms included gas passing, flatulence, diarrhea and abdominal pain and coexistence of irritable bowel syndrome (IBS).RESULTS: The frequencies of dairy intolerance syndromes in milk, yoghurt, cheese and ice cream consumption were 51.1% (532), 16.6% (173), 11.7% (122) and 13.4% (140), respectively. Most severe symptoms for milk, yoghurt, cheese and ice cream intolerance were diarrhea (2.11±0.08), gas passing (1.56±0.09) and flatulence (1.49±0.09), respectively. Fifty (9.4%) of symptomatic respondents never drank milk. Correlation coefficient between symptoms severity and the avoidance of consumption in milk intolerance was 0.38.CONCLUSIONS: Students tolerate other dairy products better in comparison with milk. In the present study, the phenomenon as irritable bowel syndrome was not strongly associated with the severity of all symptoms in dairy intolerant persons. Also, there were weak association between the severity of symptoms with dairy consumption and avoidance, but more studies are needed to evaluate calcium absorption and osteoporosis in symptomatic cases.