Objectives:To determine the magnitude, distribution and associated ergonomic factors of upper extremities musculoskeletal disorders (UEMSD) among workers of electronic assembly in Thailand. Material and Methods: This was a cross-sectional study. 591 of 853 workers in an electronic and electrical appliance assembly factory in Bangkok, Thailand, participated in this study. A self-administered questionnaire consisting of demographic data and ergonomic factors was collected from October 2010 to January 2011. Clinical examination of each worker was performed by an occupational physician. The criteria for diagnosis of UEMSD came as a result of a consensus reached by a group of orthopedists. The associated factors were analyzed using a multiple logistic regression. Results: The point prevalence of clinically diagnosed UEMSD was as follows: radial styloid tenosynovitis - 13.03% (95% CI: 10.31-15.75), trigger finger - 9.48% (95% CI: 7.11-11.84), carpal tunnel syndrome - 8.12% (95% CI: 5.91-10.33), lateral epicondylitis - 3.38% (95% CI: 1.92-4.85), and medial epicondylitis - 1.69% (95% CI: 0.65-2.73), respectively. The adjusted odds ratio with statistical significance associated with UEMSD was as follows: high force of wrist - 1.78 (95% CI: 1.06-2.99), awkward posture of wrist - 2.37 (95% CI: 1.28-4.37) and contact stress at wrists - 1.75 (95% CI: 1.02-3.00) to develop radial styloid tenosynovitis. For trigger finger, the ratios were awkward posture of fingers - 2.09 (95% CI: 1.12-3.90) and contact stress on finger - 1.86 (95% CI: 1.04-3.34). For medial epicondylitis, it was an awkward posture of using elbows - 3.14 (95% CI: 1.10-8.95). However, this study did not find any associations between repetitive motion and any UEMSD. Conclusions: UEMSD are most commonly found in electronic assembly workers. The relevant parties should provide comprehensive ergonomic resolution for these workers.