This thesis will explore the concepts related to communication, business communication, stress and its influential factors in order to put together a list of the most common causes of stress (stressors) in working and communicating with mentally ill adults. Communication with mentally ill people is specific due to the nature of their disease and certainly acts as the provoking factor in the occurrence of stress in working environment. For this purpose, a survey was conducted in Residential Facility for Adults Care Jalžabet and Residential Facility for Adults Care Borova. These are public institutions whose primary concern is caring for the adults with intellectual and mental disabilities. The aim of the research was to investigate the influence of the negative work environment in increasing the stress levels, and if the level of stress in communicating with mentally ill people is rising if their main disease is worsening. There was also the need for compiling a list of other factors that affect the increasing of stress in the workplace. Of a total of 115 employees of both Facilities for Adults Care, 60 employees or 52.1% took part in the survey. That comprises approximately 5.1% of the population of all employees in the similar facilities for adults in the Croatian social welfare system. The survey included 51 female employees, or 85% of the respondents, while the male gender was represented with 9 people or 15% of the respondents. 45 employees (75%) in this study indicated that conflicts with colleagues adversely affect the atmosphere in the working environment, while 40 employees (66.6%) stated that effect for the conflicts with superiors. Therefore, we can conclude that negative environment does influence employees by increasing the levels of stress in employees of both Facilities for Adults Jalžabet and Borova. The total number of 46 subjects (76.7%) stated that communication with the client in psychological exarcebation has stressful effects, as well as the unpredictable behaviour in crisis (deterioration) of the client, which is listed by 43 subjects (71.7%). Therefore the conclusion is that the employees' levels of stress increase if the clients are in the state of mental exarcebation. It is also interesting that as much as 45 subjects (75%) are stressed because of the responsibility for people's lives. The interest comes out of the fact that this is the stress factor for the employees who are not in direct contact with clients all the time. The most common physical signs of stress cited are headaches and rapid heartbeat, while emotional sign of stress that employees usually feel during their duties is psychic tension. Most respondents, around 40, stated that in their institutions there is no action plan for the prevention of stress caused by work. The implication is that it would be good for the employees to educate themselves, in their own initiative, on communication skills and techniques in order to easily deal with a large amount of information from the environment and thus become more efficient in solving various problems without a stressful effect as soon as possible.