Attention-deficit hyperactivity disorder (ADHD) is one of the most commonly studied and frequently diagnosed psychiatric disorders in children. It is a heritable behavioural disorder associated with cognitive impairments of response inhibition, sustained attention and working memory among others. The majority of parents and teachers notice a deficit in the perception of time in those diagnosed with ADHD, but up until now this deficit has not been objectively examined with regard to its relationship with many other impairments in ADHD. Furthermore, this is the first time a comparison of the subtypes of ADHD (Combined and Inattentive) has been explored with regard to time perception, sustained attention, response inhibition, spatial neglect, temporal order judgement, intra-individual variability and medication. A strong case is made that the ADHD-Inattentive subtype must be diagnosed and treated quite differently to the ADHD-Combined subtype.