This study examines the longitudinal course and predictors of stress-specific and general symptomatic distress in emergency services personnel. A three-group quasi-experimental design was used to determine the responses of 322 rescue workers to the Loma Prieta earthquake Interstate 880 Freeway collapse and to unrelated control critical incidents. Self-report questionnaires, including measures of incident exposure, peritraumatic dissociation and emotional distress, and current symptoms, were administered 1.9 years (initial) and 3.5 years (follow-up) after the freeway collapse. Despite modest symptom improvement at follow-up, rescue workers were at risk for chronic symptomatic distress after critical incident exposure. Peritraumatic dissociation accounted for significant increments in current posttraumatic stress disorder symptoms, over and above exposure, adjustment, years of experience, locus of control, social support, and general dissociative tendencies. The results suggest that rescue workers, particularly those with more catastrophic exposure and those prone to dissociate at the time of the critical incident, are at risk for chronic symptomatic distress.