Psoas abscess is an uncommon condition with vague clinical presentation. It generally has an insidious onset and before the advent of computed tomography, few cases were reported in the medical literature. We report the case of a middle aged diabetic woman who presented with left leg swelling. Doppler ultrasound revealed thrombosis of the popliteal vein and a collection in the left groin. Computed tomography confirmed the presence of a large left iliopsoas abscess extending to the anterior compartment of the thigh complicated with thrombosis of the superficial femoral and popliteal veins. We suggest that an iliopsoas abscess should be excluded when an immunocompromised patient presents with deep vein thrombosis.