Background: Crystal deposition is one of the most common arthropathies among the elderly. Similarly, osteoarthritis (OA) considers the most common joint pathology amongst the elderly; it is usually associated with significant pain, disability, and even synovitis. Objective: The aim of the work was to detect Crystals in Non-symptomatized crystal arthropathy in cases of primary knee Osteoarthritis. Patients and Methods: 50 patients with primary knee osteoarthritis who diagnosed according to the American College of Rheumatology classification criteria for osteoarthritis. Patients underwent to history taking, clinical examination, laboratory examination, knee US, plain radiography and synovial fluid analysis. Results: Fifty patients (35 females, 15 males) were enrolled. Mean values were 65.4 years ± 13.5 SD for age and 50.7 months ± 35.5 SD for disease duration. Plain radiography revealed chondrocalcinosis in 4 patients (8%). Crystals were detected by US in 36 knees (72%), 24 patients had calcification characteristic of CPPD and 12 patients had calcifications characteristic of MSU crystals deposition. synovial fluid examination revealed crystal deposition in 38 knees (76%), it was MSU in 12 patients and CPPD in 26 patients. The sensitivity of US for the detection of calcification was (83.3%) while that of plain X-ray was (22.2%), and the specificity was (93.8%) and (90.2%) respectively. There is statistically significant difference between patients with crystal deposition and patients without crystal deposition as regard WOMAC stiffness score. Conclusion: Subclinical crystals were detected in a significant number of Primary Knee Osteoarthritis Patients. US showed high specificity and acceptable sensitivity for the diagnosis of Crystal Arthropathy.