•Mental disorders among first-year Spanish university students are common.•35.7% of students screened positive for 12-month mental disorder.•Depression and generalized anxiety disorder are the most frequent disorders.•29.2% of students with mental disorders report severe role impairment.•12.6% of students with mental disorder receive mental health treatment. The university period carries risk for onset of common mental disorders. Epidemiological knowledge on mental disorders among Spanish university students is limited. To estimate lifetime and 12-month prevalence, persistence and age-of-onset of mental disorders among Spanish first-year university students, as well as associated role impairment and mental health treatment use. First-year university students (N=2,118; 55.4% female; mean age=18.8 years) from five Spanish universities completed a web-based survey, screening possible DSM–IV mental disorders (major depressive episode(MDE), mania/hypomania, generalized anxiety disorder(GAD), panic disorder(PD), alcohol abuse/dependence(AUD), drug abuse/dependence(DUD), and adult attention-deficit/hyperactivity disorder(ADHD)). Role impairment and treatment associated with mental disorders were assessed. Lifetime and 12-month prevalence of any possible mental disorder was 41.3%(SE=1.08) and 35.7%(SE=1.05), respectively. Persistence (i.e., ratio of 12-month to lifetime prevalence) was 86.4%(SE=1.58). Median age-of-onset was 14 for adult ADHD, 15 for mood disorders and AUD, and 16 for anxiety disorders and DUD. One third (29.2%) of 12-month disorders were associated with role impairment. Twelve-month PD (OR=4.0;95%CI=1.9-8.5) had the highest odds for role impairment. Only 12.6% of students with 12-month disorder received any mental health treatment. Twelve-month treatment was the highest among those students with 12-month GAD (OR=7.4;95%CI=3.7-14.8). The assessment of mental disorders was based on self-reports. Cross-sectional nature of the data prevents causal associations. One third of Spanish university students report a common mental disorder in the past year, and one third of those report severe role impairment. Only one out of eight students with 12-month mental disorders receives mental health treatment.