Fibrous histiocytomas can be differentiated into malignant fibrous histiocytoma or benign fibrous histiocytoma (BFH) and may involve soft tissue and hard bony tissue. A BFH is a rare group of tumors involving fibrocystic and histiocytic elements. Although BFH after a mosquito bite is rare, it must be a part of the differential diagnosis in unresponsive cases of insect bite reactions. A 57-year-old woman with a history of hypertension arrived at the clinic to discuss an 18-year-old lump in her left leg. The patient described the mass as painless and immobile on the anterior part of the left leg. She stated that it had started with a mosquito bite 18 years ago. The woman visited the clinic after her cat scratched the nodule and the erythema on the anterior area of her leg intensified. Physical examination revealed a 10 × 5 × 5 cm solid, stemmed, non-tender mass with erythema on the left leg. A CT scan revealed a stemmed soft tissue mass with well-defined borders. BFH is one of the common types of histiocytoma that is differentiated based on location, which can be dermis, subcutaneous tissue, and deep soft tissues. BFH is predominantly common in young-to-middle-aged females compared to males. BFH can emerge anywhere on the body. However, the occurrence on the lower extremities is high. This case is presented for its rarity and uncommon site of involvement and the significant clinical presentation and emerging condition following a mosquito bite.