Data regarding cancer risk for individuals who were exposed to traumatic and stressful life events are conflicting. We sought to evaluate the association between posttraumatic stress disorder (PTSD) and the risk of the four most common solid tumors: lung, breast, prostate, and colorectal cancers. We conducted four nested case-control studies using a large UK population-based database. Cases were defined as individuals with any medical code for the specific malignancy. For every case, we used incidence-density sampling to match four controls by age, sex, practice site, and both duration and calendar time of follow-up. Exposure of interest was any diagnosis of PTSD prior to cancer diagnosis. The odds ratios (ORs) and 95% confidence intervals (CIs) for cancer risk associated with PTSD were estimated using multivariable conditional logistic regression and were adjusted for smoking status, obesity, and antidepressant use. The study population included four case groups according to cancer type. There were 19,143 cases with lung cancer (74,473 matched controls), 22,163 cases with colorectal cancer (86,538 matched controls), 31,352 cases with breast cancer (123,285 matched controls), and 27,212 cases with prostate cancer (105,940 matched controls). There was no statistically significant association between PTSD and cancer risk among any of the cancer types: lung, OR = 0.73, 95% CI [0.43, 1.23]; breast, OR = 0.73, 95% CI [0.52, 1.01]; prostate, OR = 1.24, 95% CI [0.87, 1.77]; and colorectal, OR = 1.05, 95% CI [0.68, 1.62]. Our findings indicated that participants in our study with PTSD were not at increased risk of lung, breast, prostate, and colorectal cancers.