Background Practice guidelines for childhood posttraumatic stress disorder (PTSD) recommend trauma‐focused psychotherapies, mainly cognitive behavioral therapy (CBT). Eye movement desensitization and reprocessing (EMDR) therapy is a brief trauma‐focused, evidence‐based treatment for PTSD in adults, but with few well‐designed trials involving children and adolescents. Methods We conducted a single‐blind, randomized trial with three arms (n = 103): EMDR (n = 43), Cognitive Behavior Writing Therapy (CBWT; n = 42), and wait‐list (WL; n = 18). WL participants were randomly reallocated to CBWT or EMDR after 6 weeks; follow‐ups were conducted at 3 and 12 months posttreatment. Participants were treatment‐seeking youth (aged 8–18 years) with a DSM‐IV diagnosis of PTSD (or subthreshold PTSD) tied to a single trauma, who received up to six sessions of EMDR or CBWT lasting maximally 45 min each. Results Both treatments were well‐tolerated and relative to WL yielded large, intent‐to‐treat effect sizes for the primary outcomes at posttreatment: PTSD symptoms (EMDR: d = 1.27; CBWT: d = 1.24). At posttreatment 92.5% of EMDR, and 90.2% of CBWT no longer met the diagnostic criteria for PTSD. All gains were maintained at follow‐up. Compared to WL, small to large (range d = 0.39–1.03) intent‐to‐treat effect sizes were obtained at posttreatment for negative trauma‐related appraisals, anxiety, depression, and behavior problems with these gains being maintained at follow‐up. Gains were attained with significantly less therapist contact time for EMDR than CBWT (mean = 4.1 sessions/140 min vs. 5.4 sessions/227 min). Conclusions EMDR and CBWT are brief, trauma‐focused treatments that yielded equally large remission rates for PTSD and reductions in the severity of PTSD and comorbid difficulties in children and adolescents seeking treatment for PTSD tied to a single event. Further trials of both treatments with PTSD tied to multiple traumas are warranted.