Legitimacy theory as an explicator of longitudinal and cross-sectional variability in social and environmental disclosure is explored using a content analysis based method. Annual corporate reports are examined for ten UK FTSE 100 companies in five sectors over the year 1974 to 2000 by extracting word count data into the three categories of employee welfare, community and environmental disclosure. Eight hypotheses are generated, some of which are adapted from previous studies, to ''test for'' legitimacy theory. Three hypotheses test for intersectoral difference by disclosure category, three test for intrasectoral agreement by category and two test for correlation between environmental disclosure over time and environmental group membership in the UK.The ability of the study to yield certainty of explanation upon demonstration of hypotheses is constrained by the epistemogically ''semi-hard'' or ''indicative-only'' quality of the data. Data analysis is carried out and conclusions are drawn within these constraints.Evidence for a legitimacy-based explanation of disclosure variability is found where the categories are sufficiently resolved and circumscribed to discriminate by sector. In this study, community and environmental disclosure demonstrate this and thus provide evidence for a legitimacy-based explanation of social disclosure whilst employee welfare disclosure is found to be a less useful category for this purpose.