The main aim of this study was to examine the relationship between assertiveness and emotional problems (depression, anxiety and social anxiety) and burnout in physician, nurses, orderlies and ambulance drivers in the Critical Care and Emergency Services (CCES). 315 Healthcare workers completed the Assertion Inventory, the Beck Depression Inventory II, the Beck Anxiety Inventory, and the Maslach Burnout Inventory. The results show that 17.7% were not assertive, 16.6% had social anxiety, 12.9% suffered from depression, and 11.7% from anxiety. There were some sex differences. Furthermore, 52.7% had depersonalization, 46.7% felt a lack of personal accomplishment, and 24.4% suffered from emotional exhaustion. Assertiveness was significantly associated with social anxiety, exhaustion and lack of personal accomplishment. Regression analysis indicated that the lack of assertiveness was a risk factor for these three psychological difficulties. These results support the importance of including assertiveness training as part of the training of CCES professionals.