A possible outbreak of beriberi occurred at a drug detention and rehabilitation centre, Pusat Serenti Bukit Cabang, Perlis, Malaysia in February 2004. This outbreak was identified following the presentation of a large number of inmates at a health centre with signs and symptoms of ankle oedema and shortness of breath. Further investigations revealed the death of three inmates at the General Hospital with similar clinical presentations during the period from October 2003 till February 2004. A cross sectional comparative study was carried out at the rehabilitation centre to find out the prevalence of thiamine deficiency among the inmates both symptomatic and asymptomatic. A total of 154 inmates were examined (57 symptomatic and 97 asymptomatic cases). It was found that 74% from the sample study (114 cases) had thiamine deficiency (44 symptomatic and 70 asymptomatic). Further statistical analysis showed that ankle oedema is consistent with the diagnosis of thiamine deficiency but lack sensitivity (p < 0.05, sensitivity 24.6%, specificity 95%). This outbreak could have been triggered by poor diet intake of thiamine by the inmates coupled with possible intake of certain thiamine antagonists in their diet.