Since the 1970s, the various manifestations of mental health problems among Western employees have multiplied. This paper explores how occupational health physicians’ perceive the changes that have enabled the emergence of mental health concerns in the Finnish welfare regime. The interpretations of health professionals with long working careers (41 in-depth interviews of Finnish occupational health experts) are placed in a conflictual social arena, in which the tendencies of medicalization and informalization frame professionals’ work in the changing context of working life, culture and medical practice. The results emphasize three historical transformations: (1) the loosening of the stigma related to mental health problems (informalization of mental health problems), (2) the changing character of employees/patients (psychologically aware customers) and (3) the paradox of a new medical culture (decreasing medical dominance and increasing medicalization). This article demonstrates the ambiguity health professionals faced when patients with psycho-emotional health issues entered their occupational territory. It shows how the experiences of mental health professionals reflect the informalization of social contacts and conflicting tendencies related to medicalization. These are manifested in the social relationship between doctor and patient, the labelling of mental health problems and the medical culture related to mental health.