An observational study was carried out on 2595 Northern Ireland civil servants who attended a workplace lifestyle and physical activity assessment programme involving self-reported lifestyle history, measurement of physiological parameters and a 6 month follow-up postal questionnaire survey. Almost two-thirds of participants did not engage in regular moderate physical activity, with females twice as likely not to than men. Approximately one in six participants were smokers and three-quarters were found to have body fat estimations above the acceptable level, with females much more likely to be obese than men. Aerobic capacity was below average in 17% of participants and was associated with increasing age, smoking in the under 35s and poor physical activity levels. Excessive alcohol intake was found in 8% of all participants, and was more likely in men and smokers. In the follow-up survey, 83% needed to make one or more changes to their lifestyle. Smoking was the most difficult to change, with only 14% remaining abstinent after 6 months. Almost two-thirds were maintaining improved dietary habits and exercise activity, with around one-half moderating alcohol intake and achieving weight reduction. Overall, the average level of non-attempted behaviour change was one in five (19.6%), tried but failed accounted for almost one in three (31.2%) and successful maintenance of positive lifestyle change occurred in one-half (49.2%). Brief lifestyle and physical activity assessment programmes are effective interventions in getting employees to modify their lifestyles. The impact this has on wider organizational issues such as absenteeism and productivity needs further evaluation.