Strongyloidiasis is a parasitosis characterized by persistent infection before dissemination and the development of potentially fatal disease. Since diagnosis is difficult, knowledge of the prevalence and geographic distribution of the disease is of practical importance. A study was made of Strongyloides stercoralis infection in a random and representative sample of farm workers in a tourist region in Spain based on the detection of larvae of triple stool samples. The prevalence of infection was 12.4% (95% confidence interval [CI] = 8.4-16.4). None of the 26 clinical or epidemiologic variables analyzed were found to be predictive of infection. Only eosinophilia (> 400 eosinophils/mm3) was significantly greater among the infected individuals (odds ratio = 73.4, 95% CI = 16.3-327.0), with a sensitivity of 93.5% and a specificity of 93.1%. A screening program is proposed to detect eosinophilia, to provide treatment without stool examinations, and thus afford a cost-effective policy for preventing the development of severe forms of the disease among specific risk groups where the prevalence of other parasitoses is low.