Objective: Significant amount of childhood ADHD continue to have symptoms in adulthood. The objective was to determine the prevalence of adult ADHD diagnosis among psychiatry outpatients in a university hospital and to make a comparison between the cases with confirmed and probable adult ADHD in terms of various clinical features. Methods: All consecutive patients of 18-44 years old admitting to general psychiatry outpatient clinic of Karadeniz Technical University, Medical School were offered a screening with adult ADHD Self Report Scale (ASRS-v1.1) Part A. The confirmed diagnosis of adult ADHD diagnosis was made through clinical interviews according to DSM-IV criteria and established in case of positive childhood history. All diagnoses were approved by a second trained psychiatrist. Results: Four or more darkly shaded boxes within ASRS-v 1.1 Part A was marked for 21.1% (n=208) of 985 patients. Clinical interviews were offered to 181 of 208 patients. Among 181 patients 27% (n=48) of them were diagnosed with a confirmed adult ADHD, 73% (n=133) were diagnosed with probable diagnosis. Discussion: Probable cases can be regarded as subclinical form which is not easily differentiated from the confirmed cases by contrasting in comorbidity and functionality. The results of this study may indicate clinical significance which can give rise to subsequent studies.