Child sexual abuse (CSA) is a risk factor for mental illness, which might influence jurors' judgments in CSA trials.We apply expectation violation theory to explore the influence of victim mental illness and expert testimony on mock jurors' case judgments in a CSA mock trial.We expected mock jurors would perceive an alleged CSA victim with a mental illness diagnosis of posttraumatic stress disorder (PTSD) or depression as more plausibly abused than a victim with no diagnosis, and in turn, be more conviction-prone. We also expected that expert psychologist testimony (vs. no expert testimony) would elicit greater pro-victim case judgments (e.g., guilt).Participants (N = 235, Mage = 39; 52 % women; 64.5 % White) were recruited on Prolific.Participants rendered case judgments after reading a summarized CSA mock trial in which the victim's mental illness and a psychologist's expert testimony presence were experimentally manipulated in a 3 (victim mental illness diagnosis: PTSD, depression, no diagnosis) X 2 (expert testimony: present vs. absent) between-subjects design.Although there were no effects of expert testimony, mock jurors perceived the defendant as less credible (Mdiff = ±0.44, SE = 0.18, p = .035, 95 % CIs[-0.8616, -0.0251]), and were more likely to convict (Mdiff = ±23.93, SE = 9.83, p = .041, 95 % CIs[0.7329, 47.1296]) when the victim was diagnosed with PTSD versus depression or no mental illness. Perceived defendant credibility mediated the effect of victim PTSD diagnosis on increased conviction rates, Indirect Effect = 4.93(2.87), 95 % CIs[0.37, 11.46].These results suggest that victim PTSD diagnoses might increase convictions in CSA cases.