Adherence of participants in a long-term clinical trial is necessary to assure validity of findings. This article examines adherence differences between single-parent and two-parent families in the Childhood Asthma Management Program (CAMP). Adherence was defined as the percentage of completed daily diary cards and scheduled study visits during the course of the trial. Logistic regression and ordinal logistic regression analyses were used. Children from single-parent families had a lower percentage of completed diary cards (72% vs. 84%) than two-parent families. Single-parent families were also more likely to reschedule visits (62% vs. 45%) and miss more clinic visits (23% vs. 17%) than two-parent families. Suggestions are given for study coordinators to assist participants in completing a long-term clinical trial. Many suggestions may be adapted for nurses in inpatient or outpatient settings for assisting parents of patients with chronic diseases.