Objective: The enthesitis in psoriasis may be underestimated by clinical evaluation so we investigated the presence of synovitis, tenosynovitis and enthesitis with Power Doppler (PD) and ultrasonography (US) in patients with early psoriatic arthritis. AlthoughIL-23 has been implicated in the pathogenesis of Psoriasis, it was unclear how it promotes enthesitis. Aim: 1. To explore the serum level of Il-23 as a marker for disease activity in patients with active psoriatic arthritis (PsA) with enthesopathy. 2. To determine the reliability of the Madrid Sonographic Enthesitis Scoring Index (MASEI) and power Doppler (PD) technique in the assessment of enthesopathy. Methods: A total of60patients with early psoriatic arthritis of less than one year duration and 30 age corresponding healthy controls were prospectively recruited from dermatology and rheumatology departments of Zagazig university hospitals. They underwent dermatological and rheumatological assessment and a blinded US evaluation. Clinical assessment was done including demographics, severity of psoriasis and musculoskeletal clinical examination. Levels of serum IL-23 were measured for patients and controls by ELISA. Results: A total of 720 entheseal sites in 60 patients with psoriasis were examined by US.In 182 of 720 (25.2%) entheseal sites, grayscale US establishedat least 1 sign indicative of enthesopathy. In the control group, US found at least 1 sign indicative of enthesopathy in 34 of 360(9.7%). MASEI score in PsA group is 15.15 ± 6.13 and in healthy group 2.04 ± 1.19,USsynovitis and enthesopathy were significantly more common in patients than in controls. In 60PsA patients, the increased serum IL-23 level was found to be correlated significantly with inflammatory parameters and the number of swollen joints. Patients with active PsA had significantly higher IL-23 levels than patients with low inflammatory status and controls. Significant positive correlation between the level ofIL-23 and MASEI score was found in patients with PsA. PsA patients. In our study, serum IL-23 has been demonstrated to be an indicator for disease activity in patients with PsA and was correlated with MASEI score.