The diagnosis of systemic lupus erythematosus (SLE) depends on clinical evidence of renal, rheumatologic, cutaneous, and neurologic involvement, supported by serological markers. A previously healthy 14-year-old girl presented with Libman-Sacks endocarditis involving the aortic valve as the first manifestation of SLE. Even though she did not satisfy the American College of Rheumatology criteria for diagnosing SLE, she had anemia, proteinuria, elevated erythrocyte sedimentation rate, low complement 4 (C4) levels, and strongly positive antinuclear antibody titer. A renal biopsy showed stage IV lupus nephritis. Treatment was initiated with immunosuppressants and steroids. This type of presentation may be misdiagnosed as infective endocarditis missing the underlying collagen vascular disease.