The impact of five-month basic military training on body weight and fat mass was studied in 197 male obese recruits, aged 17 to 19 years old. The training programme of five days per week lasted for 20 weeks. Of these sessions, 57% could be considered to be physically intense for the obese subjects. No dietary restriction was imposed. The cohort was divided into three categories based on their percentage body fat, i.e. %BF 24 to < 30, %BF 30 to < 35 and %BF > or = 35. The overall mean weight loss was 12.5 kg or 0.63 kg per week. Mean weight losses for each category were 10.7 kg, 13.1 kg and 16.1 kg, respectively. Most of this weight was lost in the 2nd month of training. The weight loss is attributed to a decrease of body fat as determined by skinfold measurements. Attrition rate, due to training injuries resulting in temporary disabilities, was negligible at 6.1%. In conclusion, this study shows that intense physical activity over a duration of 20 weeks is effective in reducing the body fat of our obese subjects and in training obese subjects for combat duties.