BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) in girls in Europe is poorly understood; it is not known whether they exhibit similar symptom patterns or co-existing problems and receive the same type of treatment as boys. OBJECTIVE: To examine gender differences for referral patterns, social demographic factors, ADHD core symptomatology, co-existing health problems, psychosocial functioning and treatment. METHODS: Baseline data from the ADHD Observational Research in Europe (ADORE) study, a 24-month, naturalistic, longitudinal observational study in 10 European countries of children (aged 6-18 years) with hyperactive/inattentive/impulsive symptoms but no previous diagnosis of ADHD, were analysed by gender. RESULTS: Data from 1,478 children were analysed: 231 girls (15.7%) and 1,222 boys (84.3%) (gender data missing for 25 patients). Gender ratios (girl:boy) varied by country, ranging from 1:3 to 1:16. Comparisons showed few gender effects in core ADHD symptomatology and clinical correlates of ADHD. Compared with boys, girls had significantly more parent-rated emotional symptoms and prosocial behaviour and were more likely to be the victim of bullying and less likely to be the bully. Girls and boys had similar levels of co-existing psychiatric and physical health problems, and received the same type of treatment. CONCLUSIONS: Fewer girls than boys are referred for ADHD treatment, but they have a similar pattern of impairment and receive similar treatment.