Stress and stress-related disorders have been on the increase both in the UK and worldwide. UK Governmental bodies have proposed guidelines for managing stress at work; however most are aimed at reducing and preventing stress in employees. There are also a number of stress management programmes in place (including self-help), but very few have been empirically validated in a middle management population. A novel stress self-help manual based on cognitive behavioural therapy was developed for middle managers and evaluated in this randomised controlled trial (RCT; N = 102). Four outcome measures were used to measure change: Brief Symptom Inventory (BSI; primary outcome measure), Symptom Assessment-45 (SA45), Coping Inventory for Stressful Situations (CISS), and the Job Stress Survey (JSS). Treatment effects were evaluated using analyses of covariance (ANCOVA) with post- treatment scores as dependent variables and pre-treatment scores as covariates. Significant changes were obtained on the BSI (P<0.001) at post-treatment, as well as on the SA45 (P<0.001) indicating intervention effectiveness regardless of the frequency of work stressors and lack of organisational support remaining unchanged. Measures of coping indicated that the intervention increased task, emotion, and distraction-oriented coping styles (P<0.001). The intervention was not found to effect the avoidance- oriented or social diversion coping styles. Regression analyses indicated that discussing the manual with others during the treatment protocol had a significant effect on outcomes, suggesting that future interventions should encourage groups within organisations rather than individual participation, or using the manual as an adjunct to various forms of psychological therapy. Qualitative data was also collated, which revealed that the participants felt more in control and confident after working through the manual. While further evaluation by independent researchers is recommended, including cost effectiveness analysis, the manual has shown initial effectiveness and is considered a potentially useful tool for the development of improvements towards managing and preventing stress.