Introduction: Formaldehyde is a naturally occurring compound extensively used as cadavers' preservative in medical schools anatomy departments. The International Agency for Research on Cancer (IARC) classifies formaldehyde as carcinogenic to humans (group 1). Aim of the work: To examine duration of exposure as a determining factor in genotoxicity of formaldehyde exposure using the micronucleus test, correlate clinical manifestations with genotoxic effects, and measure formaldehyde air levels in dissecting rooms of Alexandria Faculty of Medicine, Egypt. Materials and methods: A pre-designed questionnaire was filled for each subject to assess clinical signs and symptoms of exposure and to screen for exclusion criteria. Buccal epithelial cells were collected; twice from 40 undergraduate students before and after one month of exposure, and once from 10 staff members who had participated in anatomy classes. Cells of both groups were stained using Feulgen method and micronucleus test (MN) was applied. The air levels were measured in 3 anatomy labs using MIRAN-IR. Results: Mean frequency of micronuclei was significantly higher in staff group (2.60 ±1.26)/1000 cells than the control and student groups (0.80±0.76)/1000 cells, (1.05 ±1.28)/1000 cells respectively with p= 0.001. Significant positive correlation between frequency of MN and skin, eye and respiratory symptoms. The mean level of airborne formaldehyde in 3 dissecting rooms was 7.2 ±6.9 ppm which is above OSHA recommendations. Conclusion: Duration of exposure is an important determinant in genotoxiciy of formaldehyde exposure. Clinical manifestations of formaldehyde exposure were correlated to the MN frequency. Studied participants are exposed to high concentrations of formaldehyde above the standard levels according to time of exposure. Efforts have to be made to improve air quality and reduce exposures during anatomy classes.