Background Expressive writing about a traumatic event is promising in treating posttraumatic stress disorder (PTSD) symptoms in adult trauma survivors. To date, the comparative efficacy and acceptability of this approach is uncertain. Therefore, we aimed to examine the comparative efficacy and acceptability of expressive writing treatments. Methods We included 44 RCTs with 7724 participants contributing 54 direct comparisons between expressive writing (EW), enhanced writing (i.e. including additional therapist contact or individualized writing assignments; EW+), PTSD psychotherapies (PT), neutral writing (NW), and waiting-list control (WL). Results EW, EW+, PT, and NW were statistically significantly more efficacious than WL at the longest available follow-up, with SMDs (95% CI) of -0.78 (-1.10 to -0.46) for PT, -0.81 (-1.02 to -0.61) for EW+, -0.43 (-0.65 to -0.21) for EW, and -0.37 (-0.61 to -0.14) for NW. We found small to moderate differences between the active treatments. At baseline mean PTSD severity was significantly lower in EW+ compared with WL. We found considerable heterogeneity and inconsistency and we found elevated risk of bias in at least one of the bias dimensions in all studies. When EW+-WL comparisons were excluded from the analyses EW+ was no longer superior compared with EW. Conclusions The summarized evidence confirms that writing treatments may contribute to improving PTSD symptoms in medium to long-term. Methodological issues in the available evidence hamper definite conclusions regarding the comparative efficacy and acceptability of writing treatments. Adequately sized comparative randomized controlled trials preferably including all four active treatment approaches, reporting long-term data, and including researchers with balanced preferences are needed.