Past studies have demonstrated that increases in cortisol secretion are associated with either enhancements or impairments of long-term memory, depending on the subprocess involved. However, working memory is generally studied as a unified system within the cortisol literature. The present study sought to determine if cortisol increases are positively associated with increases in performance in the encoding subprocess of working memory, and whether increases are positively or negatively associated with performance changes in the maintenance subprocess. Thirty-three young men (M = 19.4 years, SD = 0.89) participated in a change-detection task, consisting of a condition requiring encoding only and a condition requiring both encoding and maintenance. To elicit a cortisol response, participants completed the Trier Social Stress Test (TSST) between two administrations of the task. Cardiovascular measurements and saliva samples were obtained before the TSST (T1), and mid-way between blocks of the second administration of the change-detection task (T2), to measure autonomic and cortisol responses to the TSST evident during the second change-detection task. Cortisol increases between T1 and T2 were positively correlated with both encoding (r(32) = 0.503, p = 0.003) and maintenance (r(32) = 0.463, p = 0.007) performance. This is a novel finding as previous studies have shown an impairing effect of cortisol on working memory. The positive relation between cortisol and working memory has likely been obscured in previous tasks, which did not examine these specific subprocesses in isolation from each other. The beneficial role of cortisol in the stress response is discussed.