Women have smaller cortisol responses to psychological stress than men do, and women taking hormonal contraceptives (HC+) have smaller responses than HC- women. Cortisol secretion undergoes substantial diurnal variation, with elevated levels in the morning and lower levels in the afternoon, and these variations are accompanied by differences in response to acute stress. However, the impact of HC use on these diurnal relationships has not been examined. We tested saliva cortisol values in 744 healthy young adults, 351 men and 393 women, 254 HC- and 139 HC+, who were assigned to morning (9:00 am) or afternoon (1:00 pm) test sessions that were held both on a rest day and on a stress day that included public speaking and mental arithmetic challenges. Saliva cortisol responses to stress were largest in men and progressively smaller in HC- and in HC+ women (F = 23.26, p < .0001). In the morning test sessions, HC+ women had significantly elevated rest day cortisol levels (t = 5.99, p ≪ .0001, Cohen's d = 0.95) along with a complete absence of response on the stress day. In the afternoon sessions, both HC+ and HC- women had normal rest-day cortisol levels and normal responses to the stressors. Heart rates at rest and during stress did not vary by time of day or HC status. Cortisol stress responses in HC+ women are absent in the morning and normal in size by early afternoon. Studies of stress reactivity should account for time of day in evaluating cortisol responses in women using hormonal contraceptives.