Obstetric complications have been associated with a number of mental disorders. In this study, we investigate how obstetric complications relate with clinically significant determinants of adult attention deficit hyperactivity disorder (ADHD), such as gender, age of diagnosis, psychiatric co morbidity, severity of symptomatology and general functioning. Presence of obstetric complications as reported in the psychiatric history of 64 patients in transition from adolescence to adulthood referred to the Yorkshire service for adults with ADHD between June 2009 and October 2010 were recorded. The presence or not of these complications was examined as a factor determining a number of clinically significant variables, such as gender, age at first diagnosis, psychiatric comorbidity, severity of symptomatology (measured with Conners Adult ADHD Rating Scale (CAARS)) and general functioning (measured using the DSM-IV General Assessment of Functioning (GAF) index). Obstetric complications were not associated with any of the variables examined. Adults with ADHD in transition to adult services were highly symptomatic and disabled with a mean Conner’s score (n = 56) of 30.5 (SD = 12.8) and the most common frequency of the GAF score (n = 55) on the 60–51 range. Although it has been reported that environmental factors are associated with ADHD, the presence or absence of obstetric complications in an adult ADHD population was not associated with a number of proxy measures clinically associated with organic aetiology in mental health conditions. Future research on etiology and etiopathology should focus on prenatal and genetic factors instead.