Background: The objective of this study was to evaluate whether the distinction between leiomyosarcomas (LMS) and sarcomas with myogenic differentiation (SMD), based on the expression of muscular markers, has any clinical implications. Methods: Patients with localized LMS (excluding any gynecologic subtype) or SMD who underwent surgery at the authors' institution from 1994 to 2010 were analyzed. Overall survival (OS) and the crude cumulative incidence of local recurrence and distant metastasis (DM) were calculated, and multivariable analyses for DM and OS were carried out. Results: In total, 327 patients were studied (71% LMS, 29% SMD). The median follow-up was 58 months (interquartile range, 31-97 months). The 5-year overall survival rate was 72.9% (95% confidence interval, 66.3%-80.2%) for the patients with LMS and 64.4% (95% confidence interval, 53.7%-77.1%) for the patients with SMD. The 5-year crude cumulative incidence of distant metastasis was 36.2% (95% confidence interval, 30.1%-43.5%) in the LMS group and 32.6% (95% confidence interval, 24%-44.2%) in the SMD group. Although tumor grade in LMS identified 3 distinct classes of risk, patients with grade 2 and grade 3 SMD had a similar course. The median postmetastasis survival was longer in patients with grade 3 LMS compared versus patients with grade 3 SMD (31 months vs 15 months, respectively). In patients who had grade 3 lesions, adjuvant chemotherapy yielded a better outcome in the SMD group compared with the LMS group (hazard ratio, 0.38). Patients who had superficial LMS had better outcomes compared with patients who had superficial SMD. Conclusions: The current results indicated that LMS and SMD do not share the same natural history. A limited prognostic impact of grade was observed in patients with SMD. Differences in response to chemotherapy should be taken into account in planning the therapeutic approach for patients with these tumors. The current clinical observations may correspond to the biology of a different disease and deserve further study.