Longitudinal research produces more reliable evidence concerning causality by gathering data directly from participants, preintervention and postintervention, utilizing 1 or more follow-up studies at the conclusion. The process of surveying at different points in time ameliorates direction-of-effect problems. While there are considerable benefits when conducting longitudinal research, potential problems associated with subject attrition, also known as mortality, tend to reduce or overwhelm the benefits. This article describes attrition and its potentially detrimental consequences to the validity of a study, provides an overview of the information required to properly report attrition rates, and evaluates the commonly found attrition-reporting procedures in health education and health promotion.