Tobacco use and resultant health effects have been described as an epidemic that progresses through the population. This paper aims to describe and explain trends in lung cancer mortality by ethnicity and socioeconomic position in New Zealand between 1981-1999. Cohort studies of the entire New Zealand population for 1981-84, 1986-89, 1991-94, and 1996-99 (linking census and mortality datasets) allowed direct determination of trends in lung mortality by income and education. For ethnicity, we used unlinked census and mortality data--but with correction factors applied for undercounting of Maori and Pacific deaths. Lung cancer mortality decreased in males and increased in females over the time period studied. In males, socioeconomic inequality persisted despite a decline in mortality in all socioeconomic groups. In females, a disproportionate increase in the mortality of lower socioeconomic groups compared to higher socioeconomic groups resulted in an increase in inequality. Divergent trends by ethnic group resulted in an increase in ethnic inequalities between 1981 and 1996 in both males and females. There are significant and growing ethnic and socioeconomic inequalities in lung cancer mortality in New Zealand. In the current absence of concerted public health action these inequalities will probably widen in future decades.