OBJECTIVES An economic analysis of cost-equity (from society's viewpoint) for evaluating the impact of Law 100/93 in Colombia between 1998 and 2005. METHODS An economic analysis compared costs and equity in health in Colombia between 1998 and 2005. Data was taken from the Colombian Statistics'Administration Department (Departamento Administrativo Nacional de Estadistica - DANE) and from national demographic and health surveys carried out in 2000 and 2005. Information regarding costs was taken from the National Health Accounts'System. Inequity in Health was considered in line with the Inequity in Health Index (IHI). Incremental and average cost-equity analysis covered three sub-periods; 1998-1999 (during which time per capita gross internal product became reduced in Colombia), 2000-2001 (during which time total health expense became reduced)and 2001 -2005. RESULTS An unstable tendency for inequity in health becoming reduced during the period was revealed. There was an inverse relationship between IHI and public health spending and a direct relationship between out-of-pocket spending on health and equity in health (Spearman, p<0.05). The second period had the best incremental cost-equity ratio. CONCLUSIONS Fluctuations in IHI and marginal cost-equity during the periods being analysed suggested that health spending and equity in health in Colombia were related during the period being studied.