The current cross-sectional study examined the relationship between affiliate stigma and externalizing and internalizing problems by investigating the role of family cohesion among adolescents having a parent with serious mental illness (SMI). One hundred sixty-four adolescents were recruited from two community mental health centers. Family cohesion, affiliate stigma, and adolescent internalizing and externalizing problems were assessed. A significant relationship was found between adolescent externalizing and internalizing problems and family cohesion (
r
= −0.462,
p
< 0.01 and
r
= −0.534,
p
< 0.001, respectively) and affiliate stigma (
r
= 0.512,
p
< 0.01 and
r
= 0.656,
p
< 0.001, respectively). Family cohesion partially mediated the relation between affiliate stigma and externalizing problems (
Z
= −4.97,
p
< 0.001) and fully mediated the relation between affiliate stigma and internalizing problems (
Z
= −5.18,
p
< 0.001). The current study highlights the need for effective interventions aimed at families to support parents with SMI in their parenting role and enhance family cohesion. [
Journal of Psychosocial Nursing and Mental Health Services, 57
(12), 39–47.]