Background: There are conflicting reports about the effect of psychological stress upon menstruation. We studied menstrual patterns and stress in 254 undergraduate medical students. Method: All girls of years one and two were included. The students maintained menstrual records over six months. DASS questionnaires measured stress. Salivary cortisol levels were also measured. Results: In year 1 and 2 students, persisting normal cycles were 39.4% and 36.5%; normal becoming abnormal were 28.8% and 23.1%; abnormal becoming normal were 19.2% and 17.3%; persisting abnormal were 12.5% and 23.1% . Students with moderate to severe stress (20% and 21%) had less stress at six months (13% and 15%) Comment: Most students have normal menstrual patterns, and no stress. Stress if present tends to decrease with time. There is no clear association between psychological stress and menstrual abnormality. Keywords : Menses; stress; medical students; DASS score eISSN 2514-7528 © 2017 The Author. Published for AMER ABRA by e-International Publishing House, Ltd., UK. This is an open-access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer–review under responsibility of AMER (Association of Malaysian Environment-Behaviour Researchers), ABRA (Association of Behavioural Researchers on Asians) and cE-Bs (Centre for Environment-Behaviour Studies), Faculty of Architecture, Planning & Surveying, Universiti Teknologi MARA, Malaysia.