This article reviews the most common and characteristic mesenchymal lesions found in the gastrointestinal tract and intraabdominal location in a pattern-based approach: spindle and epithelioid tumors (gastrointestinal stromal tumor, schwannoma, glomus tumor, leiomyoma and leiomyosarcoma, inflammatory fibroid polyp, perineurioma, melanoma, calcifying fibrous tumor, sclerosing mesenteritis, mesenteric fibromatosis, and inflammatory myofibroblastic tumor), and clear and granular tumors (clear cell sarcoma, granular cell tumor, gangliocytic paraganglioma, and ganglioneuroma). Information includes gross and histologic features, diagnosis and differential diagnosis, and histologic and other diagnostic techniques, including immunohistochemistry related to projected patient outcome, along with prognosis, staging, and treatment.