OBJECTIVES: Health Related Quality of Life (HRQL) following lung transplantation (LGTX) becomes more important with increased life expectancy. Analyses are often hampered by a relatively large number of patients who drop out, due to their condition or death. This problem of missing values is of real importance, and cannot be neglected. In the present study the change in HRQL before and after LGTX was analysed as a function of several predictors, assuming that the probability of missing only depended on the observed measurements (Missing at Random). METHODS: Between 1992 and 2002, 415 patients completed one or more self-administered HRQL questionnaires before and up to 63 months after LGTX. The questionnaires were sent by mail on a regular basis. In this study we focus on one dimension of the energy Nottingham Health Profile. A multi-level model was used to analyse the changes in this dimension as a function of several predictors. Since multi-level structures do not require balanced data to obtain efficient estimates, all patients who completed at least one questionnaire were taken into account. RESULTS: The dimension energy of the NHP improved significantly after LGTX. This remained more or less constant up to 63 months after LGTX. The predictors 'age' and 'the presence of Bronchiolitis Obliterans Syndrome (BOS)' appeared to have a significant influence. For pre- and post-transplantation patients, the scores on the dimension energy increased with age. This means that older patients have more restrictions regarding energy than younger patients. After the onset of BOS, patients experienced significantly more restrictions in the NHP energy measure. CONCLUSION: There are considerable improvements regarding the NHP dimension energy after lung transplantation. Age and BOS are highly significant predictors. The improvements are maintained during long-term follow-up.