Objective: The purpose of this study was to determine whether the presence of obesity was related with symptoms of nocturnal enuresis (NE) and the efficacy of behavioral intervention in the treatment of NE. Materials and Methods: The patients diagnosed with primary monosymptomatic nocturnal enuresis (PMNE) were studied retrospectively. NE severity was classified as mild, moderate, and severe according to the frequency of enuresis. The children were divided into three groups, namely normal weight (5th-84th percentile), overweight (85th-94th percentile), and obesity (>= 95th percentile), according to their Body Mass Index (BMI) percentage. The relationship between obesity level and enuresis severity was analyzed. After three months of behavioral therapy, the efficacy of treatment among normal, overweight, and obese groups were evaluated. Moreover, the predictive risk factors for treatment failure were investigated. Results: The rates of severe enuresis in patients with normal weight, overweight, and obesity were 63.9%, 77.5%, and 78.6%, respectively. Obese children depicted higher odds of having severe enuresis compared with normal-weight children (OR: 1.571; 95% confidence interval [CI]: 1.196-2.065; P=0.001). The odds of presenting with severe enuresis were 1.99 times higher in children who are obese or overweight compared to children with normal weight (OR: 1.994; 95% CI: 1.349-2.946; P=0.001). The complete response of the normal group was higher than those of the overweight and obese groups (26.8% vs. 14.0%, P=0.010; 26.8% vs. 0.0%, P=0.000). Overweight children showed higher complete response than obese ones (14.0% vs. 0.0%, P=0.009). Logistic regression analysis revealed that obesity level and enuresis frequency were significantly related to the treatment failure of behavioral intervention. Conclusions: Obesity is associated with severe enuresis and low efficacy of behavioral therapy in children with nocturnal enuresis.