The aim of this study, was to compare the prevalence of sleeping problems in two ethnically different populations living under the same extreme arctic climate. A total of 453 Norwegians (319 males and 134 females) were compared with 450 Russians (317 males and 133 females), all aged 18 years or older, living on Svalbard, the northernmost regular settlement in the world. Among Russians, 81% of the male subjects and 77% of the female subjects reported sleeping problems lasting for at least 2 weeks. The corresponding figures for the Norwegians were 22% (for males) and 25% (for females). Among Russians, sleeping problems decreased with increasing age, but no such age trend was found in Norwegians. Whereas sleeping problems among Norwegians were approximately equally frequent throughout the year, the Russians reported more problems during the polar night. 'Problems falling asleep', 'not feeling rested in the morning' and 'walking up several times during the night' were the most frequent types of sleeping problems in both groups. Depression, shift work, loneliness, ability to concentrate, alcohol consumption and quality of life were associated with sleeping problems in Norwegian subjects, whereas depression, shift work, ability to concentrate, and worry were associated with sleeping problems in Russians. The prevalence of sleeping problems was nearly fourfold higher among Russian subjects than among Norwegians living on Svalbard. As the Russians were recruited from a lower latitude than the Norwegians, we postulate that their problems should be interpreted in terms of inadequate acclimatization after migration to the north.