This study used the ostracism detection theory to investigate how ostracism impacts individuals in two ways: (1) immediate poststressor needs, mood, ruminative thoughts, and desire to affiliate, and (2) short‐term affective and cortisol reactivity. A total of 58 college students were randomly assigned to the inclusion or ostracism conditions of Cyberball, a virtual ball‐tossing game. Immediately following the experimental manipulation, ostracized participants reported more thwarted psychological need states, more negative mood, and fewer positive ruminative thoughts, relative to their included counterparts. Ostracized participants reported a greater interest in affiliating with others in online or in‐person settings. In the short‐term, ostracized males reported more hostility than included males, although the scores were within expected norms for most males. There was no relation between Cyberball condition and gender across time for depression, anxiety, or positive affect. Approximately 20 min after the onset of the stressor, women in the luteal phase and women taking oral contraceptives in the ostracized group displayed higher cortisol than their counterparts in the included group. Relative to baseline, however, cortisol did not reliably increase after the onset of the stressor. Ostracized females taking oral contraceptives showed the greatest decline in cortisol, compared to included oral contraceptive users. Overall, results suggest that most of the negative effects of ostracism are immediate and limited to psychological, not neuroendocrine, responses.