BACKGROUND: Behavioral sleep problems are common in children with attention deficit hyperactivity disorder (ADHD), and longitudinal studies have found sleep problems to be both a predictor and outcome of internalizing and externalizing problems. We investigated the potential bidirectional relationship between sleep problems and internalizing/externalizing problems. METHODS: Children with ADHD, aged 5-13 years, were recruited from 21 pediatric practices across Victoria, Australia (N = 270). Across a 12-month period, at three time points, parents reported on their child’s sleep problems (Children’s Sleep Habits Questionnaire) and emotional and behavioral functioning (Strengths and Difficulties Questionnaire). Data were analyzed using autoregressive cross-lagged panel models. RESULTS: Sleep problem severity and emotional/behavioral problem severity were very stable across the 12-month period. Sleep problems at baseline predicted emotional problems at six months (r = 0.17, p < 0.01), and emotional problems at baseline predicted sleep problems at six months (r = 0.07, p < 0.05). However, there was no predictive relationship between sleep problems and emotional problems from 6-12 months. No bidirectional relationship was observed between sleep problems and conduct problems. CONCLUSIONS: In children with ADHD, there is weak evidence of a bidirectional relationship between sleep problems and emotional problems. These symptoms are also very stable over time; therefore, the best treatment approach to improve overall functioning may be to target both sleep and emotional functioning in these children.