Objectives: Contemporary societal views on old age as well as a rise in retirement age raise the question whether patterns of stability and/or decline in network size as found in earlier studies similarly apply to later birth cohorts of older adults. Methods: Change score models are estimated to determine cohort differences in age-related trajectories in network size. Two birth cohorts (1928-37 and 1938-47, 55-64 at baseline in 1992 and 2002) of the Longitudinal Aging Study Amsterdam are followed across 4 observations over a time span of 9 years. Results: Age-related trajectories in network size differ between the early and late birth cohort. The late birth cohort makes large gains in network size around retirement age, but this increase does not hold over time. Increased educational level and larger diversity in social roles relate to the cohort difference. Nonetheless, cohort difference prevails even after adjusting for these factors. Discussion: The peak level in the network size in the late birth cohort hints at stronger preference and more opportunities to gain and maintain social relationships around retirement age in the current societal structure and culture. The subsequent drop-off in network size suggests that these ties are mostly used to adapt to the retirement transition. © 2018 The Author(s) 2018. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.