In a prospective study of 115 patients with systemic meningococcal disease, 61 control patients and 293 population controls, environmental and other factors which preceded the illness and which might have influenced the acquisition and case fatality rate of the meningococcal disease were investigated. Passive smoking in children under 12 year of age, stressful events, and symptoms and signs of preceding illness within the last two weeks were significantly more frequent in meningococcal patients than among the population controls. In contrast, those patients who had been exposed to stressful events, or who had symptoms or signs of ill-health preceding the meningococcal disease, had significantly reduced case fatality rates as compared to those who had not had any such experiences. Passive smoking remains a factor of great interest for further studies and intervention.