Recent psychological investigations have demonstrated the significant impact of the sibling relationship throughout the lifespan. To determine the extent of developmental consistency in sibling relationships, 62 working class adults (40 female, 22 male) were interviewed about the nature of their relationship with the sibling to whom they felt closest. The subjects were stratified by age and life period into four groups: 21 young adults (mean age, 19.4 years); 13 adults (mean age, 30.4 years); 15 middle-aged adults (mean age, 43.4 years); and 13 pre-retirement adults (mean age, 57.6 years). A 26-category system, which divided respondents' thoughts on the basis of ideas rather than grammatical structures, was used to code the interview data. An analysis of the results showed that the intimacy category was significantly higher during the two earliest periods of the adult life cycle in contrast to the middle-aged and pre-retirement periods. However, no significant age effects were obtained for the following categories: positive affect, reciprocity, compatibility, similarity, activity, instrumental support, or expressive support. The findings reflect consistency in the sibling relationship across the adult life cycle, with emotional support characterizing that bond. (BL)