Denmark is the only country in which scabies has been reported for many decades. The present study is based on 850,629 cases reported between 1900 and 1975. The incidence of scabies showed pronounced peaks around 1918 and 1945. Since the end of the 1960s, a new increase in incidence has been observed. The rates were high and rather uniform among infants, children, and young adults. Before puberty, the rate for girls was on an average 1.4 times higher than for boys. Scabies showed the same incidence in the capital as in the provinces, and marked seasonal variations occurred, with a winter maximum and a summer minimum. No single factor could be identified to explain the cyclic occurrence in time, the sex and age pattern, and the seasonal variation. These patterns probably have a multifactorial genesis!