Background. Vulnerability-stress models ascribe stress a pivotal role in the development of psychosis. However, moderating and mediating mechanisms translating stress into psychosis and the specificity of the association are not clearly established. It is hypothesized that stress will trigger paranoid ideation in vulnerable individuals through an increase in negative emotion. Method. Using a repeated-measures design, 64 healthy participants with varying levels of vulnerability [psychosis symptoms assessed by the Community Assessment of Psychic Experiences (CAPE)] were assigned to a stress and a non-stress condition in random order. Stress was induced by exposing participants to building-site noise (75 dB) applied concurrently with difficult knowledge questions. Symptoms of paranoia, depression and obsessive compulsive disorder (OCD) were assessed by state-adapted versions of clinical scales. Results. In the stress condition there was an increase in paranoia, depression and negative emotion. Multilevel linear modeling (MLM) revealed the increase in paranoia under stress to be moderated by the level of vulnerability and mediated by anxiety. Although participants generally showed an increase in anxiety under stress, anxiety was more strongly related to paranoia in participants with higher baseline symptomatology. Conclusions. The results support and specify the role of emotional reactions to stressors on the pathway from vulnerability to psychosis and highlight the relevance of anxiety.