Smokers in your office are costing your employer an extra $5,816 per year for each smoker compared to nonsmoking employees. That's the conclusion following an analysis of data collected from previous studies of smoking-related costs.

The research, conducted at Ohio State University, estimates that the largest cost for employers is related to work that does not get done when a smoker takes a smoke break. That cost alone is estimated to add $3,077 annually for each smoker compared to a non-smoker.

Smokers, on average, take about five smoke breaks during a typical work day. Most non-smokers, by comparison, take only three work breaks.
 
The NY Times blog has additional details from the study:

The second largest cost, at $2,056, was related to excess health care expenses. Smokers typically have more health problems than nonsmokers, including heart and lung disease and various cancers.

The remaining costs came from increased absenteeism — the researchers found that smokers miss about two-and-a-half extra workdays each year — and lost productivity at work, perhaps because of nicotine's withdrawal effects. The findings appeared online in June in the journal Tobacco Control.