Objective: Constraint induced aphasia therapy (CIAT) is a more intensive form of language treatment for aphasia as compared to traditional treatments. This study examined whether there are differences in cortisol stress levels between the two methods of aphasia treatment as well as effects on language skills. Design: Randomized controlled trial. Methods: A total of 20 participants with expressive aphasia were randomly placed into one of the two treatment groups. The CIAT group received 10 days of intensive treatment over two weeks. The traditional therapy group received 6 days of treatment over 2 weeks. All participants in each group provided salivary cortisol samples before treatment, at the mid-point of treatment, and at the conclusion of treatment. Language skills were assessed before treatment and at the conclusion of treatment. Results: A significantly higher proportion of individuals in the CIAT treatment group had increased salivary cortisol stress levels when compared to the traditional treatment group at the mid-point of the program (80% versus 30% respectively, p<0.05). There was no significant difference in the proportion of individuals with increased cortisol stress by the end of the treatment. Language scores for word repetition and overall aphasia quotient significantly improved for the CIAT group when compared to the traditional group (p<0.05). Conclusions: The CIAT treatment appears to initially create increased psychophysiological stress as compared to the traditional treatment. In spite of the initial increases in psychophysiological stress, participants appear to become conditioned to the challenge and ultimately have enhanced benefit from CIAT treatment.