Concerns are raised that rapid catch up growth during nutrition rehabilitation of severely malnourished children may be associated with disproportionately higher amounts of body fat deposition. This study examined the composition of weight gain in severely undernourished children who underwent nutrition rehabilitation in a hospital from India. Body composition of 80 severely malnourished children (age 6-60 months) was assessed using skin-fold thickness measurements on admission and after 1 month of supplementary feeding. On admission, children had severe weight and height deficits and were severely wasted. The mean weight for age z score, height for age z score and weight for height z score (WHZ) were -5.0, -4.2 and -4.1 respectively. Children consumed a mixed diet and mean energy intake was 177 kcal/kg/day with a protein energy ratio of 13. Overall, the mean weight gain was 6.1 g/kg/day and fat mass contributed to about 40% of the weight gain. When the composition of weight gain was analysed in tertiles of baseline WHZ score, children in the lowest tertile of WHZ score had significantly higher weight gain and fat free mass (FFM) gain. Gain in fat mass did not differ in relation to the baseline WHZ score. The study demonstrates that it is possible to achieve rapid weight gain with recovery of lost tissue in severely malnourished children with mixed diets. Children with lowest WHZ scores at baseline gained higher FFM during nutrition rehabilitation when compared to the children with relatively higher WHZ score probably in an attempt to recover the lost tissue.