This study was carried out to evaluate the role of ultrasound and power Doppler in detection and quantification of inflammatory signs of the knee joint in rheumatic patients and to correlate these findings with their clinical stage aiming to develop a sensitive method for staging disease activity and severity in rheumatic diseases affecting the knee joint. Fifty patients (twenty with RA, ten with SLE, eighteen with osteoarthritis, one with seronegative arthritis, one with reactive arthritis), who had clinical signs of knee joint involvement were included in this study. All patients were subjected to clinical examination by a rheumatologist and laboratory investigation as well as radiological examination in the form of plain radiography, grey scale ultrasonography and power Doppler sonography. Ten patients only were also subjected to MRI, as well as, ten patients with joint effusion were subjected to aspiration and injection of intraarticular steroid. Synovial thickening was demonstrated in 90% of patients with RA, 30% in SLE patients and 30/% in O.A. patients. There was a highly significant difference in synovial hypertrophy for RA (P= 0.0001). PDS detected inflammation (acute or chronic) in 100% of RA, 30% SLE, 44% O.A. There was a highly significant difference in synovial hypertrophy for RA (P= 0.0001). Correlation between clinical condition and degree of inflammation detected by PDS in patients with rheumatoid arthritis shows high significant value (P= 0.0001). Correlation between the clinical condition and sonographic findings in the form of synovial thickening in patients with rheumatoid arthritis was done. Synovial thickening was significantly higher in severe cases compared to mild cases (P=0.002) and moderate cases (P<0.001) while there was no significance in comparing the mild and moderate forms (P = 0.35). Detection of synovial effusion in the suprapatellar pouch and its extension in joint recesses shows 90% in RA, 20% in SLE, and 33% in OA. P value was 0.0001 for rheumatoid arthritis, which is highly significant. Baker’s cyst was detected in 15 patients with rheumatoid arthritis, in two of them, it was ruptured. Detection of meniscal degeneration in rheumatic patients shows in RA; MM (30%), LM (35%), in SLE; MM (10%), LM (10%) and in OA; MM (75%), LM (60%). Articular cartilage affection and presence of osteophytes in rheumatic diseases were demonstrated in RA (20%), SLE (10%), O.A. (100%). P value of osteoarthritis was 0.001 denoting high significance.