The presumptive treatment of parasitosis among immigrants with albendazole has been shown to save both money and lives, primarily via a reduction in the burden of Strongyloides stercoralis. Ivermectin is more effective than albendazole, but is also more expensive. This coupled with confusion surrounding the cost-effectiveness of guiding therapy based on eosinophil counts has led to disparate practices. We used the newly arrived year 2000 immigrant population as a hypothetical cohort in a decision analysis model to examine the cost-effectiveness of various interventions to reduce parasitosis among immigrants. When the prevalence of S. stercoralis is greater than 2%, the incremental cost-effectiveness ratios of all presumptive treatment strategies were similar. Ivermectin is associated with an incremental cost-effectiveness ratio of 1700 dollars per QALY gained for treatment with 12 mg ivermectin relative to 5 days of albendazole when the prevalence is 10%. Any presumptive treatment strategy is cost-effective when compared with most common medical interventions.