This prospective study describes the ultrasound, computerized tomography and magnetic resonance imaging findings in 16 cases of patellar tendinitis. In all cases tendon enlargement and reduced echogenicity were visible on ultrasound. Computerized tomography demonstrated enlargement of the tendon with reduced attenuation of the central portion. Magnetic resonance imaging showed focal tendon enlargement in all patients with high signal lesions in 88% of cases. This study has shown that patellar tendinitis may be identified with all three modalities. Ultrasound is recommended as the initial investigation in the assessment of patients with this condition.