Human migration is as old as the human evolution. Factors influencing migration are numerous and the number of migrants is increasing worldwide. Immigrants constitute 13.1% of the Norwegian population and 23% of the population of the capital of Norway, Oslo. Migration can be associated with increased risk of mental illness.Seasonal affective disorder (SAD) is more prevalent in populations who live in higher latitudes. SAD is described to occur more in the winter season (W-SAD) than in the summer. In addition a milder form of SAD, Sub-syndromal SAD (S-SAD) is also described in the literature. Despite the fact that SAD among immigrants found to be higher than the native population in some studies, there is a significant paucity of research on SAD among immigrants.This is the first study on SAD among the immigrants in Norway. The quantitative part of the study used the data collected among adult (31 to 60 years) immigrants living in Oslo in 2002 (The Oslo immigrant health study). The qualitative part of this study conducted in 2011, which includes eight in-depth interviews among adult Sri Lankan immigrants living in Oslo, is novel as there are very few qualitative studies to look in to seasonal affective disorder.There were significant differences in SAD prevalence rates among the five immigrant groups (Turkey; 16.9, Sri Lanka; 6.9, Iran; 21.5, Pakistan; 17.7 and Vietnam; 14.9) included in the study. W-SAD was significantly associated with country of birth, younger age, smoking, presence of mental distress, frequent visits to the psychiatrist or the General Practitioner (GP), self reported poor health and presence of chronic illnesses. Gender, Number of years living in Norway, education and employment status were not significantly associated with W-SAD. S-SAD was significantly associated with Country of birth, smoking and alcohol consumption.Sri Lankan immigrants expressed the view that seasonal changes do not affect their mood and they feel happy and contented about their physical and mental health. They also described that family, social and cultural integrity and better economic prospects as reasons behind their perceptions of happiness.In conclusion, Iranians had the highest and the Sri Lankans had the lowest prevalence of W-SAD, and prevalence of SAD is not as high as compared to other studies among immigrants. These findings were confirmed by the qualitative study, where Sri Lankan immigrants attributed lower levels of SAD to close family and social networks and better economic prospects. Further research on perception of SAD and mental health among immigrants, especially the other four groups, should be encouraged.