The life expectancy of patients with Duchenne muscular dystrophy (DMD) has increased. A cross-sectional study of DMD patients showed that 54 % of 13-year-old patients are obese and that 54 % of 18-year-old patients are underweight. We aimed to describe the natural evolution of weight status in DMD. This retrospective multi-centre audit collected body-weight measurements for seventy DMD patients born before 1992. The body-weight:age ratio (W:A) was used to evaluate weight status in reference to the Griffiths and Edwards chart. At the age of 13 years, 73 % were obese and 4 % were underweight. At maximal follow-up (age 15–26 years, mean 18·3 (sd 2·3) years), 47 % were obese and 34 % were underweight. Obesity at the age of 13 years was associated with later obesity, whereas normal weight status and underweight in 13-year-old patients predicted later underweight. A W:A ≥ 151 % in 13-year-old patients predicted later obesity, and a W:A ≤ 126·5 % predicted later underweight. Our audit provides the first longitudinal information about the spontaneous outcome of weight status in DMD. Patients (13 years old) with a W:A ≥ 151 % were more likely to become obese in late adolescence, but obesity prevented later underweight. These data suggest that mild obesity in 13-year-old DMD patients (W:A between 120 and 150 %) should not be discouraged because it prevents later underweight.