Sweet syndrome is acute eruption of tender, dull red plaques and nodules accompanied by which is common in the face, neck, and extremities. It is characterized histologically by intense focal infiltration of the dermis by polymorphonuclear leukocytes. It has been recently reported that the disease is associated with malignant tumors, and the disease as a skin marker of malignant tumor is acquiring increasing interest. A 58-year-old man was admitted to the hospital because of an early gastric cancer which was detected at a medical checkup. The patient had been noticed of a swelling of the left thumb and erythemas on the back of the neck. A pylorus preserving gastrectomy was conducted for the 2c lesion on the angular notch. No lymph nodes metastasis were noted. After the operation, erythemas on the back neck, face, anterior chest and thumb appeared, become worse, and then revealed Sweet syndrome. Steroid therapy was choiced but the effect remained to be fair, and no complete remission was achieved. Thereafter a thyroid cancer was revealed and a subtotal thyroidectomy was performed 9 months after the operation. Skin eruptions which were once aggravated after the thyroidectomy improved slightly that persist up to now. The patient should be carefully followed by paying attention to possible occurrence of blood dyscrasias. Sweet syndrome associated with malignancy has been hardly studied in a large series, especially association with solid tumor. This case of the disease combined with two solid malignant tumors is the first report in the Japanese literature.