Incomplete injuries (grade I or II) to the medial collateral ligament (MCL) of the knee are common and usually self limiting. Some patients complain of chronic medial knee pain following injury. We highlight the importance of anatomical investigation of these patients and evaluate a successful treatment technique. A consecutive case series of 34 patients with chronic pain following grade I/II MCL injury were reviewed. Injury prevented sporting activity, and examination revealed thickening and tenderness of the MCL. The knee was assessed by MRI. All patients had radiological evidence of injury to the superficial and deep MCL, with thickening, scarring and tearing. Patients were treated with ultrasound guided injection of local anaesthetic and steroid into the deep MCL and clinically reassessed. They were allowed to return to sport immediately. They were assessed for recurrence of symptoms with a postal questionnaire. Four were excluded from follow up. Four were lost. All patients reported an immediate and sustained resolution their medial knee pain. At mean follow up of 20.4 months (range 11-38 months) all were back to their pre-injury level of work. Twenty five (96%) had immediate and sustained return to sporting activity. Twenty one (81%) reported no change in level of sporting function. In patients with persistent medial joint pain following grade I/II MCL sprain, pain from the deep MCL must be considered. MRI will confirm the diagnosis, exclude coexistent pathology and localise the lesion within the deep MCL. A single corticosteroid injection provides an excellent clinical outcome 20 months post injection.