Objective: Data on incidence rates are scarce in GH deficiency (GHD). Here, we estimate the incidence rate in childhood onset (CO) and adult onset (AO) GHD in Denmark. Design: We used three national registries to identify 9131 cases with an increased risk of GHD. Date of entry was defined using the date when a registration had taken place and when a date of sufficient information could be defined from a thorough examination of a record of a GHD patient, which ever came last. We considered date of entry as the incident date. Methods: Sex-specific incidence rates of GHD in children and adults using the background population as reference. Results: During 1980-1999, 1823 patients were incident. Three-hundred and three males and 191 females had CO, 744 males and 585 females had AO GHD. The incidence rate over time was stable for females with AO GHD and increasing for the other three subgroups. Average incidence rate for CO males, 2.58 (95% confidence interval (CI), 2.30-2.88), CO females, 1.70 (95% CI, 1.48-1.96), AO males, 1.90 (95% CI, 1.77-2.04), and AO females, 1.42 (95% CI, 1.31-1.54) all per 100 000. The incidence rate was significantly higher in males compared to females in the CO GHD group (P!0.001) and in the AO GHD group in the age ranges of 45-64 and 65C years (P!0.001). There was no significant difference in the 18-44 years age group. Conclusions: In conclusion, we have identified the incidence rates of GHD in a nationwide study of Denmark. In this population-based study, we have identified in CO GHD and in the two oldest age groups of AO GHD, a statistically significant higher incidence rate in males when compared with females.European Journal of Endocrinology 155 61-71