Objective To compare mental health at 5 years in children born extremely preterm with a reference group, and assess associations between neurodevelopmental disabilities and mental health within the preterm group.

Design In a national Norwegian cohort with gestational age (GA) 22–27 weeks or birthweight 500–999g mental health was assessed with The Strengths and Difficulties Questionnaire (SDQ), cognitive function with the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R), motor function with the Movement Assessment Battery for children (ABC-test) and severity of cerebral palsy (CP) with the Gross Motor Function Classification for CP (GMFCS). Neurodevelopmental disabilities (NDD) were described as mild and moderate/severe. SDQ of the preterm children was compared with that of an unselected reference group. SDQ sub-scores ≥90^th percentile of the reference group were defined as a mental health problem and a Total Difficulties Score ≥90^th percentile (TDS90) as suggestive of psychiatric disorder.

Results Of 372 eligible preterm children parents completed SDQ for 255 (69 %). 97(38%) had TDS90 compared to 116 (11%) of the reference group (OR: 5.1; 95% CI 3.7 to 7.1). For the preterms the rate of TDS90 was higher for those with moderate/severe NDD (27/37 vs. 27/116, adjusted OR: 8.09; 95% CI 3.2–19, and mild NDD 43/102 (adjusted OR: 2.2 (1.2–4.1). For preterms with no NDD TDS90 was more common than for the reference group (27/116 vs. 116/1089, OR: 2.5; 95% CI 1.6 to 4.1).

Conclusion Extreme prematurity was associated with increased risk of later mental health problems, particularly if they had other neurodevelopmental disabilities.