Despite being widely recognized as a significant public health problem there are surprisingly few contemporary data available on the incidence of pneumonia in the UK. We conducted a general population-based cohort study to determine the incidence of pneumonia in general practice in the United Kingdom. Data were obtained from The Health Improvement Network (THIN) - a computerized, longitudinal, general practice database. Recorded diagnoses of pneumonia between 1991 and 2003 were used to calculate the incidence of pneumonia stratified by year, sex, age group and deprivation score. The overall incidence of pneumonia was 233/100 000 person-years [95% confidence interval (CI) 231-235] and this rate was stable between 1991 and 2003. The incidence of pneumonia was slightly lower in females compared to males [age-adjusted incidence rate ratio (IRR) 0.88, 95% CI 0.86-0.89]. Pneumonia was most common in children aged <4 years and adults aged >65 years. There was an increased incidence of pneumonia with higher levels of socioeconomic disadvantage such that people living in the most deprived areas of the United Kingdom were 28% more likely to get pneumonia than those in the least deprived areas (age- and gender-adjusted IRR 1.28, 95% CI 1.24-1.32). In conclusion, pneumonia is an important public health problem and the incidence of pneumonia is higher in people at the extremes of age, men and people living in socially deprived areas.