Peak incidences of giant cell arteritis (GCA) following human Parvovirus epidemics were found in 2 previous epidemiological studies. The incidence of GCA [temporal arteritis and polymyalgia rheumatica (TA + PMR)] was studied before and after a major epidemic of human Parvovirus in 1994. Clinical data from the National Patient Register showed a significant inversion of the TA/PMR ratio during a 12-month period after an HPV epidemic. The inversion of this ratio was due to an increase in TA. The change in the ratio was most pronounced in the regions with the epicenter of the epidemic.