Written emotional disclosure (WED) is a structured therapy which encourages people to write about highly emotive experiences for a pre-specified duration and number of sessions. The first studies of WED instructed undergraduate student participants to write for 20 minutes over four consecutive days about their most stressful or traumatic experiences. Since then, WED has been used in other healthy and clinical populations to varying degrees of effect. This article highlights some factors for consideration when designing a trial of WED. Specifically, the importance of intervention-related factors (e.g. number, spacing and duration of sessions, positive vs. negative disclosure, emotionally ‘neutral’ control tasks), potential moderators and analyses are discussed. The number of writing sessions (at least three are advised), duration of writing, time of day, privacy afforded to participants and appropriate control writing are highlighted as particularly important in the design of WED trials.