Lipomatous soft-tissue tumors are the most common neoplasms encountered by physicians. They range from benign lipomas to high-grade liposarcomas. Unplanned excisions of sarcomas are commonly due to the presumptive diagnosis of lipoma and can be avoided by understanding their diagnostic magnetic resonance imaging appearance. Magnetic resonance images should be obtained for all soft-tissue masses that are deep to fascia or those >5 cm in subcutaneous tissue. Atypical lipomatous tumors present as large deep fatty masses and have a propensity for local recurrence and a small risk of malignant transformation. Well-differentiated liposarcomas are histologically identical to atypical lipomatous tumors but have a markedly worse prognosis secondary to their anatomic location. Masses that lack isointense signal to subcutaneous fat on MRI may represent a sarcoma and require a biopsy before definitive treatment. Large deep lipomatous masses and liposarcomas should be sent to a sarcoma referral center for definitive treatment.