Empirical evidence of no age-related decline in life satisfaction (LS) in old age contrasts with frequently observed declines in the objective quality of elder people's lives and has therefore been labelled a "paradox" and interpreted in terms of stability of LS in the respective gerontological discussion. However, as this evidence was mainly derived from cross-sectional age group comparisons, it does neither clearly indicate the absence of age-related mean level change, nor intra-individual stability of LS. Thus, the development of LS in middle and late adulthood was analysed longitudinally by using data from the German Socio-Economic Panel. Based on single item measures of LS across 16 repeated panel waves with one per annum (1984-1999), autoregressive (quasi-Markov) structural equation models were used to estimate true score variances and intra-individual true score stability in one-year intervals. Research questions concerned (a) "monotonic" stability and variance in a subsample of old respondents (born before 1925) as compared to the total sample and (b) change in stability and variances in old age. Results indicate high "monotonic" true score stability of LS over the whole adult life span, whereas mean levels declined slightly in old age. No striking evidence for age-related changes in variance or stability was found.