Guided by the monitoring process model (MPM), the authors explored the illness responses of 2 samples: high monitors (who are cognitively vigilant to and amplify threat-related cues) and low monitors (who avoid them and blunt their impact). Both samples-101 women with human papillomavirus-related precancerous cervical dysplasia and 75 HIV-infected gay men-were undergoing long-term medical follow-up and management. Structural equation analysis showed an adequate fit of the MPM to the data within each sample, supporting the model's heuristic value: High monitors experienced greater disease-related intrusive ideation, which triggered greater avoidant ideation to forestall panic, particularly in the more threatened HIV-positive sample. However, efforts to avoid disturbing intrusive thoughts were ineffective, requiring increasingly extreme defensive strategies (i.e., denial and mental and behavioral disengagement).