To elucidate the histopathological features of laterally spreading gastrointestinal stromal tumors (GISTs), we retrospectively examined 52 GISTs grossly completely resected from 50 patients. Laterally spreading features were identified in 7 GISTs (13%), and were localized within non‑thickened regions of the muscularis propria adjacent to the main GISTs, ranging in length from 0.12 to 0.7 cm (mean, 0.3 cm). The laterally spreading features involved the muscular surgical margins in 2 cases. The morphologies of the laterally spreading cells resembled those of tumor cells in 4 cases, but were comprised of more slender spindle cells with smaller nuclei compared with those in the respective main GISTs. Compared with the main GISTs, KIT+ and discovered on GIST 1+ immunostaining features of the spreading lesions were similar in 4 cases, and were weaker or diminished in the other 3 cases. There were no differences in CD34+ staining features between the main GISTs and the laterally spreading lesions. One patient with laterally spreading GIST succumbed to the disease 2.5 years after the surgery, while the other 6 patients were alive without the recurrence of disease 0.4‑19.2 years after the surgery. The laterally spreading features were associated with a pedunculated GIST (P=0.006), but not older age (P=0.312), sex (P=0.969), tumor size (P=0.430), mucosal invasion (P=0.666) or higher risk category (P=0.872). Results of the present study indicate that resection of a ≥1‑cm muscular safety margin, and not mucosa or submucosa, is required for microscopically negative surgical margins, particularly for pedunculated GISTs.