OBJECTIVE: Diagnosis of obesity using traditional body mass index (BMI) using length may not be a reliable indicator of body composition in spina bifida (SB). We examine traditional and surrogate measures of adiposity in adults with SB, correlated with activity, metabolic disease, attitudes towards exercise and quality of life. DESIGN: Adult subjects with SB underwent obesity classification using BMI by length and arm span, abdominal girth and percent trunk fat (TF) on dual energy X-ray absorptiometry (DXA). Quality of life measures, activity level and metabolic laboratory values were also reviewed. RESULTS: Among eighteen subjects (6 male, 12 female), median age was 26.5 (range 19-37) years, with level of lesion 16.7% =L2, 61.1% L3-4, and 22.2% >/=L5, respectively. Median weight was 71.8 (IQR 62.4, 85.8) kg, similar between sexes (P = 0.66). With median length of 152.0 (IQR 141.8, 163.3) cm, median conventional BMI was 29.4 m/kg2, with 7 (43.8%) subjects with BMI >30. Median BMI by arm span was 30.2 m/kg2, abdominal girth of 105.5 cm, and TF 45.7%. More subjects were classified as obese using alternate measures, with 9 (56.3%) by arm span, 14 (82.4%) by abdominal girth and 15 (83.3%) by TF (P = 0.008). Reclassification of obesity from conventional BMI was significant when using TF (P = 0.03). No difference in quality of life measures, activity level and metabolic abnormalities was demonstrated between obese and non-obese subjects. CONCLUSIONS: Conventional determination of obesity using BMI by length is an insensitive marker in adults with SB. Adults with SB are more often classified as obese using TF by DXA.