Oslo, the capital of Norway, has a population of 500,000. Living conditions vary considerably within the city, and the mortality rate in the most deprived area is almost three times as high as in the most affluent one. We wanted to explore how morbidity varies within Oslo. We used four town-wide disease registers to study the prevalence of the four diseases in the most deprived and the most affluent part of the city. We found that tuberculosis occurs more frequently in the poor area, while type 1 diabetes mellitus in children occurs more frequently in the most affluent area. For multiple sclerosis and rheumatoid arthritis we could not find any differences between the areas.