Smoking is to blame for half of the difference in death rates between men in the top and bottom social classes, say international researchers.
Widespread smoking cessation could halve the gap
In England, Wales, the US, Canada and Poland, men of lower social class, income or education have a two-fold increased risk of dying earlier.
More than half of this involved differences in smoking-related death risk, they found.
Experts said the Lancet study showed the impact stopping smoking could have.
Professor Sir Richard Peto, co-author from the University of Oxford, said: "Widespread cessation of smoking could eventually halve the absolute differences between these social strata in the risk of premature death."
Focusing on smoking cessation might be a quicker and simpler fix than tackling other causes of social inequalities.
Michael Marmot, from the International Institute for Society and Health at University College London, said: "The conclusion might be to forget social conditions, neighbourhood deprivation, employment conditions, early childhood and subsequent adult disease, just focus on getting the smoking rates down in people of low status."
Cancer Research UK's medical director Professor John Toy said: "All men who smoke play Russian roulette with their lives but the odds are heavily stacked against those in lower income groups as they are much more likely to smoke.
"This study, part-funded by Cancer Research UK, shows that social inequality in death rates demands attention, concentrating on ways to help less privileged people to stop smoking."
Sir Richard and colleagues estimated the number of deaths among men aged 35-69 that could be attributed to smoking and those not attributed to smoking in three social bands in four countries using mortality data from 1996.
They found on average a 19% difference between the highest and lowest social strata in the risk of dying in each country and about half of the difference was due to the risk of being killed by smoking.
Ian Wilmore, of Action on Smoking and Health, said: "Smoking is the number one contributor to health inequalities because it accounts for at least half of the difference in life expectancy between the social classes.
"If you are a man in social class E, the poorest social group, your chance of surviving until the age of 70 is about one in two. If you are a man in social class A, the highest group, your chance is about two in three.
"Encouraging people to quit is the number one public health intervention that will help to deal with health inequalities. That is why comprehensive smoke-free legislation is needed."
A spokesman for the British Heart Foundation, said: "We know there are black spots of heart disease in deprived areas, and it's increasingly clear that smoking is a major cause of these variations.
"We're supporting projects to encourage smokers to quit right across the country,
"We will continue to call on the government to offer tailored smoking cessation services to give smokers the best possible chance to quit."