The objective of this article is to help clinicians interpret trial-based quality of life (QOL) changes over time. We address a series of questions and provide guidelines that are fundamental to assessing and interpreting change. The issues addressed are as follows: (1) What are the characteristics of the population for whom changes in QOL are reported? (2) Is the QOL questionnaire reliable, valid, and responsive to change? (3) Are the timing and frequency of assessments adequate? (4) Is the study adequately powered? (5) How are multiple QOL outcomes addressed in analyses? (6) How are multiple time points handled? (7) Can alternative explanations account for the observed change or lack of observed change (eg, handling of missing data, survival differences, and changes in patient's QOL perspective over time)? and (8) How is statistical significance translated into meaningful change? These guidelines will support clinicians in reviewing the clinical trial literature, which in turn can help them use the data in the treatment decision process.