A 34-year-old man with peripheral eosinophilia, chronic pruritus, and colonic eosinophilic infiltration is presented as a patient-oriented problem-solving case report to show the important aspects of differential and specific diagnosis, treatment, prognosis, and caveats in the approach to the workup of the patient with eosinophilia. Allergic rhinitis, asthma, atopy, and drug-induced eosinophilia should come to mind in the initial differential diagnosis of any patient with peripheral eosinophilia. Also included in the differential after allergic disease processes would be the general categories of infectious, neoplastic, and the various forms of organ-specific eosinophilic infiltration and idiopathic syndromes. The importance of ruling out infectious causes for eosinophilia is paramount, especially given the dangers of immunosuppressive treatments often used to treat other conditions associated with eosinophilia.