This prospective study examined the individual and combined influences of 4 poor health behaviors (smoking, low fruit and vegetable intake, high alcohol consumption, and a low level of physical activity) on total and cause-specific mortality. A representative sample of 4886 men and women 18 years and older from across the United Kingdom was followed up for 20 years (1985-2005). A simple health behavior score was developed, allocating 1 point for each poor behavior. During the follow-up period, 1080 participants died, 431 from cardiovascular diseases, 318 from cancer, and 331 from other causes. Adjusted hazard ratios for total mortality associated with 1, 2, 3, and 4 poor health behaviors compared with none were 1.85, 2.23, 2.76, and 3.49, respectively (P for trend, <.001). The combined effect of poor health behaviors on mortality was substantial, indicating that modest but sustained improvements to diet and lifestyle could have public health benefits.