Background: Mid-dermal elastolysis is a rare entity defined by the selective loss of elastic tissue in the mid dermis. Many cases appear induced or aggravated by ultraviolet (UV) light exposure. Pathogenesis is still uncertain. Objective: Our purpose was to report on the clinical and histologic features of 11 patients with mid-dermal elastolysis. Moreover, we analyzed by immunohistochemistry leukocyte subsets and expression of metalloproteinase (MMP) with the potential to degrade elastic tissue in 7 cases. Results: All patients were women with a mean age of 31.4 years. Disease duration ranged from 4 months to 17 years. Affected areas included the trunk, neck, and upper aspect of limbs. Two patients also had Hashimoto's thyroiditis and uterine carcinoma, respectively, whereas 1 patient had undergone silicone mammoplasty. In all patients, disease onset was associated with intense UV light exposure. Moderate leukocyte infiltration in the dermis was observed mostly in recent lesions and was composed of CD3⁺ T cells and some CD68⁺ macrophages with a normal number of factor XIIIa⁺ dermal dendritic cells. Elastin, but not fibrillin-1 immunoreactivity disappeared from the mid dermis. MMP-9 was detected in epidermal keratinocytes and in the cytoplasm of large, angulated, multinucleated cells located in lesional dermis. These cells were negative for leukocyte, dendritic cell, macrophage, and T-cell markers and were absent in old lesions. Staining for MMP-7 and MMP-12 did not differ from control skin. Conclusion: Onset of mid-dermal elastolysis appears strongly associated with UV exposure, which may induce fibroblast-like cells to express MMP-9 that in turn could be involved in the degradation of elastic fibers. (J Am Acad Dermatol 2003;48:846-51.)