OBJECTIVES: To describe the associations between a range of demographic, family and clinical factors and clinician-rated measures of global impairment in children with ADHD symptoms obtained at the baseline assessment in the ADHD Observational Research in Europe (ADORE) study. METHODS: Global impairment was measured by clinicians using the Clinical Global Impression-Severity (CGI-S) scale and the Children's Global Assessment Scale (CGAS). Associations with independent variables were investigated using forward-stepwise regression models. RESULTS: For the CGI-S and CGAS analyses, complete data sets were available for 1,265 and 985 children, respectively. The baseline mean CGI-S score in this population was 4.4 (SD 0.9) and the mean CGAS score was 55.0 (SD 10.6). Factors significantly associated with increased impairment on both outcome measures were: increased severity of ADHD symptoms, increased peer relationship problems and presence of oppositional defiant disorder and/or conduct disorder. Also, the presence of anxiety and/or depression and the presence of somatic symptoms were associated with increased impairment on CGI-S,while family health problems and premature birth were associated with increased impairment on CGAS. CONCLUSIONS: The severity of clinician-rated impairment in the ADORE sample is increased by the presence of disruptive behaviour problems and emotional problems, somatic symptoms, peer relationship difficulties, family health problems and premature birth.