Aims/hypothesis The aim of this study was to assess the association between all-cause mortality and sex, age at diagnosis and year of diagnosis in Norwegian patients with childhoodonset diabetes. Methods The study was based on the nationwide, populationbased Norwegian Childhood Diabetes Registry, which includes all newly diagnosed cases of childhood-onset diabetes at age 0-14 years in 1973-1982 and 1989-2012 (n=7,884). Patients were followed until date of death, emigration or 30 September 2013. Results Among the 7,884 patients, representing 132,420 person-years, 249 (3.2%) died during a mean follow-up of 16.8 (range 0.0-40.7) years. The standardised mortality ratio (SMR) for the total cohort was 3.6 (95% CI 3.1, 4.0), increasing by attained age. Absolute mortality was significantly lower in females than in males (HR 0.50 [95% CI 0.38, 0.65]), although the SMRs were similar. Cox regression analysis showed a significant decrease in mortality of 49% (HR 0.51 [95% CI 0.28, 0.93]) for those diagnosed in 1999-2012 compared with those diagnosed in 1973-1982 (p=0.03). Conclusions/interpretation In spite of improved diabetes care, mortality is still three to four times higher in those with childhood-onset diabetes compared with the general population in Norway. However, absolute mortality has declined among children diagnosed most recently (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) compared with those diagnosed in the earliest period (1973)(1974)(1975)(1976)(1977)(1978)(1979)(1980)(1981)(1982).