Background: “Dermal hypersensitivity reaction” (DHR) is diagnosed by dermatopathologists but is not an accepted clinical disease entity. There are no clear guidelines for its diagnosis, differential diagnosis, or management. Objectives: The objectives were to define the histologic criteria for cases histologically diagnosed as DHR and identify corresponding clinical disorders. Methods: Skin biopsy specimens from 130 patients diagnosed as “consistent with DHR” were reviewed. Additional information was obtained from patients, their dermatologists, and medical records. Results: Follow-up in 74 of 110 patients (median, 26.6 mo) revealed, most commonly, diagnoses of urticaria, drug reactions, and spongiotic (eczematous) dermatitis. Among the remaining cases, 37 of 59 reported persistence of disease, some exhibiting a uniform phenotype characterized by excoriated, edematous papules on the trunk. Histopathologic features present in more than 90% of 143 biopsy specimens included superficial and mid-perivascular lymphocytic infiltrates with eosinophils. Conclusion: DHR is a perivascular lymphocytic dermatitis with eosinophils involving the papillary and upper reticular dermis and minimal, if any, primary epidermal alteration. The term DHR does not represent any known clinical disorder; rather, it corresponds to many clinical disorders. The use of the phrase “dermal hypersensitivity reaction pattern” may be helpful in conveying the idea that a particular histologic pattern may be seen in a number of clinical disorders. (J Am Acad Dermatol 2002;47:898-907.)