The aim of our study was to describe the occurrence of Acute Intermittent Porphyria (AIP) in Denmark demographically, genetically and biochemically.The study was based on a database of porphobilinogen deaminase (PBGD) mutations detected in the period of 2000-2010. A total of 148 individuals were registered (90 (61%) women, 58 (39%) men). 14 of these had died during the period, and three had emigrated (the latter were excluded from further analysis). The geographical distribution of PBGD mutation carriers was based on their addresses (five Danish regions, Greenland and Faroe Islands) at the end of the study period. PBGD mutations were detected by standard exon and splice site sequencing procedures.The biochemical diagnosis of an acute porphyria attack was based on a PBG/creatinine ratio of ≥5.0 mmol/mol (reference interval 0.0–0.8 mmol/mol). Demographic distribution and prevalence: Region of Denmark Populations number Number of different mutations Number of carriers identified Approximate prevalence Capital 1.662.285 7 16 1:104.000 Zealand 821.252 7 17 1:48.000 South 1.194.659 12 36 1:33.000 Central 1.247.732 5 27 1:46.000 North 580.515 6 18 1:32.000 Greenland 56.061 2 2 1:28.000 FaroeIsl. 48.644 1 15 1:3.000 Total 5.611.148 22 131 1:43.000 The average age of the 131 PBGD mutation carriers still alive at the end of the observation period was 47 years (2-97) (men; 44 years (2-97), women; 49 years (5-94)). Of these individuals 25 (19%) had obtained a biochemical diagnosis of AIP (6 (11%) men, 19 (26%) women). The total amount of measurements of biochemistry significant for acute porphyria attack in the registration period was 366, which corresponds to an average of 15 (1-83) per individual (32 (2-83) among the men, 9 (1-41) among the women) The 14 individuals who died during the registration period showed a higher prevalence of biochemical diagnosis of AIP (43%). Interestingly, they were all women showing a shorter mean lifespan (68 years, range 44-93) than the general female population (80.78 years). In total, 22 different PBGD mutations were discovered, the mutations were widely distributed across regions, with the striking exception of the Faroe Islands, where all 15 individuals carried the same mutation (c.498+1G>A, p.splicedefect). The prevalence of PBGD mutation was very high in the Faroe Islands (1:3000).However, for the rest of the country the prevalence was comparable to or lower than the prevalence reported in several other countries (Sweden (10:100.000),Finland (3:100.000),USA (4:100.000), and Western Australia (3:100.000)). 1. Bylesjö I. Epidemiological, clinical and pathogenetic studies of Acute Intermittent Porphyria. Dissertation, Umeå University. 2008.