OBJECTIVE: To describe the self-reported mental health of New Zealand secondary school students in 2012 and to investigate changes between 2007 and 2012. METHODS: Nationally representative health and wellbeing surveys of students were completed in 2007 (n=9107) and 2012 (n=8500). Logistic regressions were used to examine the associations between mental health and changes over time. Prevalence data and adjusted odds ratios are presented. RESULTS: In 2012, approximately three-quarters (76.2%, 95% CI 74.8-77.5) of students reported good overall wellbeing. By contrast (also in 2012), some students reported self-harming (24.0%, 95% CI 22.7-25.4), depressive symptoms (12.8%, 95% CI 11.6-13.9), 2 weeks of low mood (31%, 95% CI 29.7-32.5), suicidal ideation (15.7%, 95% 14.5-17.0), and suicide attempts (4.5%, 95% CI 3.8-5.2). Between 2007 and 2012, there appeared to be slight increases in the proportions of students reporting an episode of low mood (OR 1.14, 95% CI 1.06-1.23, p=0.0009), depressive symptoms (OR 1.16, 95% CI 1.03-1.30, p=0.011), and using the Strengths and Difficulties Questionnaire – emotional symptoms (OR 1.38, 95% CI 1.23-1.54, p<0.0001), hyperactivity (OR 1.16, 95% CI 1.05-1.29, p=0.0051), and peer problems (OR 1.27, 95% CI 1.09-1.49, p=0.0022). The proportion of students aged 16 years or older reporting self-harm increased slightly between surveys, but there was little change for students aged 15 years or less (OR 1.29, 95% CI 1.15-1.44 and OR 1.10, 95% 0.98-1.23, respectively, p=0.0078). There were no changes in reported suicidal ideation and suicide attempts between 2007 and 2012. However, there has been an improvement in self-reported conduct problems since 2007 (OR 0.78, 95% CI 0.70-0.87, p<0.0001). CONCLUSIONS: The findings suggest a slight decline in aspects of self-reported mental health amongst New Zealand secondary school students between 2007 and 2012. There is a need for ongoing monitoring and for evidence-based, accessible interventions that prevent mental ill health and promote psychological wellbeing.