Sjögren-Larsson syndrome (SLS), originally described in Sweden, has been studied in a countrywide survey. A total of 58 SLS patients in 41 families were traced, 35 of them still alive. Thirty patients, 23 alive and seven deceased, have not been reported earlier. The mean incidences per 100,000 in the years 1901-1977 were 0.6 in the whole of Sweden, 10.2 in the county of Västerbotten and 2.7 per 100,000 in the county of Norrbotten. In the above-mentioned areas, the prevalence figures of SLS on 31st December 1978 were estimated to be 0.4, 8.3 and 2.6 per 100,000 persons, the frequencies of SLS gene carriers 0.5, 2.0 and 1.0%, and the gene frequencies 0.002, 0.010 and 0.005, respectively. Of the 58 identified Swedish SLS patients, 45 were born in a restricted area in the northeast of Sweden.