Instability of the patella occurs when it fails to track fully in the femoral groove during knee movement. The groove begins at the metaphysis of the distal femur and extends on its anterior surface inferiorly to the femoral notch. It is normally present at birth and the cartilaginous shape is similar to that of the adult. An abnormal trochlea may be shallow. In extreme cases it may be dome-shaped, where it is associated with recurrent subluxation or dislocation of the patella. In these cases it is logical to consider fashioning a groove as part of a realignment procedure. This study reports the operative technique and early clinical and radiological results of a consecutive case series of the first 15 patients (17 knees) who underwent a deepening trochleoplasty for severe dysplasia developed from that described by Dejour. The follow-up was for a minimum of 1 year (average 3 years, range 1 to 9 years). The boss height was reduced from an average of 7.5 mm (range 6 to 11 mm) to 0.7 mm (range -1 to 3 mm). Tracking became normal in 11 knees and had a slight J-shaped in six. Seven knees had mild residual apprehension. Seven patients were very satisfied, six were satisfied, and two were disappointed. The Kujala score improved from an average of 48 (range 13 to 75) to 75 (range 51 to 98) out of 100 (p<0.05). Three patients returned to full sports. Eight patients required further operations apart from the removal of metallic screws in 10 knees. Five of these were arthroscopic arthrolysis for stiffness at about 6 weeks post-operatively. Trochleoplasty for severe dysplasia of the femoral sulcus is a developing procedure. It requires careful attention to detail. For a rare condition the early results have been satisfactory with an acceptable level of complications.