Abstract Adherence markers provide new kinds of clinical trial data. Adherence data on individual participants obtained from markers can be used for designing the trial sample size and stratification, evaluating the adequacy of randomization, directing the management of adherence, and analyzing and interpreting the trial's final results. Examples of these are presented. Analyses of adherence data can employ conventional procedures. Box plot techniques are proposed for flogging extreme values of the distribution of adherence either at a single time point or in a time continum. The effect of differences in distribution of the markers in two or more groups in a clinical trial is discussed. Survival analysis is illustrated as one technique in univariate and multivariate analysis of markers with covariate effects. Design considerations with markers in a clinical trial are discussed, with particular emphasis on some of the assumptions and biases that must be considered for the analysis.