Background: Publication bias occurs when positive results are more likely to be published. It can profoundly affect the uptake of results of systematic reviews. Objectives: To assess the prevalence of positive results and examine factors potentially influencing the results in randomized clinical trials (RCTs) of acupuncture. Methods: We systematically searched PubMed, EMBASE and the Cochrane Library to identify acupuncture RCTs published in English up to February 2014. We classified studies as having positive or negative results based on our defined criteria. We analyzed associations between positive results and independent variables such as country origin, journal type, and methodological characteristics by Chi-square. Results: We included a total of 855 RCTs from 35 countries, published from 1975 to 2014. Positive results were identified in 68.7%. The results of trials from Thailand (n=4), Greece (n=3), Belgium (n=2), Croatia (n=2), Egypt (n=1), Hungary (n=1), New Zealand (n=1) and Singapore (n=1) were all positive, followed by Spain (7/8, 87.5%) and China (191/223, 85.7%). Positive results were 82.0% of trials from eastern countries while 61.2% from western countries (P < 0.01). Positive results of trials published in complementary and alternative medical journals (77.0%) were higher than those published in general medical journals (63.5%), and professional medical journals (62.7%; P < 0.01). Single-center trials (71.8%) reported higher positive results than multicenter trials (61.1%; P < 0.01). Trials with unclear or inadequate allocate concealment reported higher positive results (71.4%) than trials with adequate allocate concealment (62.4%; P < 0.01). Acupuncture plus conventional therapy versus conventional therapy reported higher positive results (87.8%) than other comparisons (P < 0.01). Journal impact factor, sample size, trial registration, random sequence generation, blinding, funding did not affect the positive results. Conclusions: Positive results of acupuncture RCTs varied by country, journal type, and are associated with number of centers, and allocate concealment. Further efforts should be focused on transparent reporting of clinical trials.