BACKGROUND Previous analyses of published clinical trials have identified major deficiencies in reporting, design, analysis, and overall quality. The purpose of this study was to determine the strengths and weaknesses of published clinical trials in family practice, and to identify predictors of quality in these trials. METHODS Randomized controlled clinical trials published in The Journal of Family Practice from 1974 to 1991 were eligible for the study. Two raters independently evaluated the adequacy and appropriateness of reporting, design, and analysis for each clinical trial, using the Chalmers index for assessing clinical trial quality. Multiple linear regression was used to determine the predictors of quality. RESULTS The 53 trials included in the study showed deficiencies in reporting, design, and analysis, although fundamental design issues, such as blinding, were a relative strength. On average, the trials scored 35% of the possible points on the scale. Three factors were positively associated with overall quality: year of publication, number of pages of the published report, and the type of intervention. Trials with pharmacologic and non-medication therapy interventions, such as diet, had higher quality scores than did trials with psychosocial or educational interventions. CONCLUSIONS The overall quality of these clinical trials was less than optimal but comparable to previously analyzed groups of trials. The improvement in quality over time may be related to improvement in the quality of the trials themselves, or more exacting editorial standards, or a combination of the two.