ADHD is traditionally described as a pediatric disorder. According to contemporary knowledge in around 60% of children suffering from ADHD symptoms of the disorder persist into adulthood. The epidemiological data show the 2-5% prevalence of ADHD in adults. The consequences of the disorder are serious and may cause other health problems and impairments in occupational and individual functioning. The diagnosis of ADHD in adult is based on diagnostic criteria which were created for children. As a result, many difficulties and doubts appear during diagnostic process, and it may also lead to underdiagnosis of ADHD in adults. The paper presents disadvantages of the current diagnostic criteria of ADHD in adults in both DSM-IV and ICD-10. Suggestions of authorities concerning the changes, which may facilitate the diagnosis of ADHD were discussed. The most important proposals are: with reference to symptoms - the inclusion of additional symptoms describing the specificity of hyperactivity in adults and the reduction of number of symptoms, which should be fulfilled to set the diagnosis; with reference to age-onset criterion - the increase of age level (symptoms should begin before 12).