Stronger engagement of older adults in social activities and greater embeddedness in networks is often argued to buffer cognitive decline and lower risks of dementia. One of the explanations is that interaction with other people trains the brain, thereby enhancing cognitive functioning. However, research on the relationship between personal networks and cognitive functioning is not yet conclusive. While previous studies have focused on the size of personal networks as a proxy of cognitive stimulation, little attention has been paid to the complexity of the personal network. Adults embedded in a broad range of network relationships (i.e., various relationship types) are likely to be exposed to a wider range of stimuli than adults embedded in a homogeneous network including similar relationship types. We expect that higher numbers of personal relationship types rather than a higher number of similar contacts relate to higher levels of cognitive functioning and slower cognitive decline. Data are from the Longitudinal Aging Study Amsterdam (LASA) and include 2959 Dutch participants aged 54 to 85 at baseline in 1992 and six follow-ups covering a time span of twenty years. Cognitive functioning is assessed with the Mini-Mental State Examination (MMSE), and for network complexity we use the Social Network Index. We test our expectations using fixed-effects regression models. The results reveal that a reduction in network complexity is associated with a reduction in cognitive functioning, which is neither explained by size of the network nor by presence of specific relationship types. However, enhanced complexity has only a marginal buffering effect on decline in cognitive functioning. We conclude that network characteristics and cognitive functioning are intertwined and that their association is mostly cross-sectional in nature. (C) 2014 Elsevier Ltd. All rights reserved.