The observation of Strongyloides stercoralis larvae in the feces of infected patients still constitutes the most frequent diagnosis method for this parasite; nevertheless, these larvae are excreted in low number and not daily. For this reason, their visualization require the analysis of at least 5 to 7 samples collected in consecutive days and processed using methods such as the Baermann method (BM) or agar plate culture (APC). If these methodologies are not used the prevalence of S. stercoralis is under estimated. An example of that under estimation, is the prevalence reported for Costa Rica, because in the majority of surveys of intestinal parasites do not included BM nor ACP and reported a frequency less than 0.5% for S. stercoralis. However when those methods are used its prevalence is higher: 1% in patients with AIDS, 5.7% in alcoholics, and 2% in older persons. The failure to diagnose this parasitosis is reflected in the frequent reports of fatal cases associated with hiperinfections, brought about by corticosteroid therapy. The similarity between corticosteroids and an ecdisis hormone of the parasite, which promotes maturation of infective larva in the intestine of the patient, is a possible explanation for this association. The frequent reports of fatal cases due to S. stercoralis underscores the need to include methods such as BM or ACP in the diagnosis of this parasite