This longitudinal study aimed to examine acute and posttraumatic stress symptoms and predictors of traumatic stress symptoms in parents of children recently diagnosed with cancer. The sample comprised 220 parents of 143 children who completed questionnaires at diagnosis (T1) focused on acute stress disorder (ASD); of these, 145 parents of 97 children completed questionnaires 6–8 months later (T2) focused on posttraumatic stress disorder (PTSD). Demographic, psychosocial, and treatment and illness variables were predictors. Results were that 63% of mothers and 60% of fathers met criteria for ASD at T1. At T2, 21% of mothers and 16% of fathers met criteria for PTSD, with 40% of parents reporting significant subthreshold symptoms. Predictors of ASD symptoms were female gender, presence of psychosocial risk factors, trait anxiety, family functioning, and central nervous system tumor diagnosis. Risk factors for PTSD symptoms were younger maternal age, severity of ASD symptoms, and trait anxiety at T1, and parent-reported quality of life of the child at T2. The results suggest that screening for ASD may help identify parents at increased risk of persistent traumatic stress symptoms who could benefit from preventative, evidence-based psychosocial interventions.