Femoroacetabular impingement (FAI) is proposed as a leading pathomechanic cause enrolled in pathogenesis of degenerative changes that lead to osteoarthritis (OA) of hip joint. Main objective of this study is to report clinical outcome following the arthroscopic treatment of patients with FAI in the presence moderate OA in form of radiological staging (Tönnis II) hips. Twenty nine patients underwent arthroscopic surgery for FAI; all with preoperative radiological signs of Tönnis II (two separate observers’ agreement) were prospectively included in this study. With minimum one year follow-up, clinical assessment with Hip Outcome Score (HOS) and conversion rate to total hip replacement (THR) were addressed. The study included 29 patients (30 hips); 18 males, 11 females and age range was 18-61 years (mean 39.9 year). With mean follow-up 30.59 months, five patients (16.66%) had undergone total hip replacement at end point of one year, leaving 24 patients for the analysis. At last follow up, 24 patients (82.75%) reported that they were satisfied with the outcome of surgery, HOS mean preoperatively was 54.84 (average 15-93.4 points) and 77.69 (average 11.11-100 points) postoperatively with mean improvement 22.85 points. Arthroscopic treatment for patients with FAI in Tönnis II hips resulted in clinically relevant improvements regarding pain; function and quality of life in the majority of patients included in this study but leaving a considerable percentage of THR conversion at one year follow up.