The personality domains of extraversion and neuroticism are regarded as being stable individual psychological characteristics, yet it remains unclear whether they are associated with chronic disease over an extended period of time. In a randomized controlled trial of smoking cessation nested within the original prospective Whitehall Study (1967–2012), the Eysenck Personality Questionnaire was administered to 832 male self-declared smokers who had undergone a medical examination during which their levels of extraversion and neuroticism were quantified. In the 42-year follow-up period, there were 781 deaths. In analyses in which participants from both trial arms were pooled, there was little evidence of a robust relation of either personality domain with death from all causes, coronary heart disease, stroke, respiratory disease, or cancer in any of our analyses. We therefore found no support for a role of either extraversion or neuroticism as determinants of long-term mortality risk.