Sensitivity to stress has long been implicated in the pathogenesis of schizophrenia. It remains unclear, however, which exact mechanisms underlie the progression from vulnerability to psychotic breakdown. For the present study, we hypothesized that the induction of stress would aggravate cognitive biases in schizophrenia. A total of 20 acute and remitted schizophrenia patients and 15 healthy controls were tested with parallel versions of cognitive biases paradigms under 2 laboratory conditions: stress (loud noise, 75 dB) vs no-stress. In the course of both conditions, participants had to fill out a questionnaire that assessed depressive, obsessive-compulsive, and paranoid symptoms. For the patients with acute psychotic symptoms, paranoid but not other psychiatric symptoms were elevated under stress in comparison with no-stress. In contrast, stress somewhat diminished subclinical paranoid symptoms in healthy participants. Jumping to conclusions was evident in schizophrenia under both conditions but significantly more pronounced when stress was applied first in the acute group. A tendency emerged in both acute and remitted patients to attribute events to other people under stress which was not seen in healthy subjects. The present study may serve as a starting point for further research investigating how stress translates vulnerability into acute paranoia and to pinpoint cognitive risk factors that can be modified by treatment.