Attention-deficit/hyperactivity disorder (ADHD) is related to offending, however it is unclear whether offending is directly related to ADHD or whether the multiple correlates and complicating factors associated with both ADHD and offending, such as substance use and low IQ, explain offending. The current study tests whether the relationship between ADHD and offending holds after controlling for IQ, in addition to other important confounds. One-hundred and eighteen patients with a diagnosis of ADHD were separated into groups of offenders (N = 44) and non-offenders (N = 74). Groups were compared in terms of IQ, neuropsychological measures of response inhibition and attention, ADHD symptoms, conduct disordered behaviour and substance use. Logistic regression demonstrated that IQ, substance use and conduct disordered behaviour predicted offending and that a univariate relationship between response inhibition/ADHD symptoms and offending behaviour did not hold when controlling for IQ. These findings indicate that it is important to measure and control for IQ when considering offending in the context of ADHD.