BACKGROUND. Merkel cell tumor is an uncommon, aggressive neoplasm of the skin, now regarded as a neuroendocrine carcinoma. Eyelids are among the sites where it can develop, often mimicking a benign process. The purpose of this report is to describe two new cases and to discuss briefly the problems of diagnosis and treatment. METHODS. Two patients with Merkel cell tumor of the eyelids are described. In both cases, the original clinical diagnosis was chalazion. Progressive growth of the lesion identified it as a tumor some 2-7 months after it was first noticed. The patients were treated by surgical excision of the tumor tissue, and only one by a course of local radiotherapy. The visual acuity was measured with Snellen fractions. The dose of local radiotherapy is given in cGy. RESULTS. Histopathological and immunohistochemical studies identified the lesion as a neuroendocrine carcinoma, consistent with Merkel cell tumor. The natural history was marked by aggressive behavior in one case, and by a delayed recurrence in the other, requiring different therapeutic approaches. CONCLUSION. Merkel cell carcinoma of the eyelid is a tumor that ophthalmogists should be aware of, as early diagnosis is a prerequisite for successful treatment. Rapid recurrence of any chalazion in a middle-aged or elderly patient should therefore prompt its histological examination to exclude the possibility of a malignant tumor.