Background: Rheumatoid arthritis (RA) has been associated with premature immunosenescence and an increased prevalence of age-related morbidities including poor cognitive function. Objective: We explored the relationships among lymphocyte subsets and memory in RA. Methods: Thirty patients with RA and 19 age-matched healthy controls took part in this study. Cognitive function stress and depression scores were evaluated by structured clinical questionnaires. Lymphocytes were isolated and immunophenotyped by flow cytometry to investigate the following subsets: B cells, activated and naïve/memory T cells, regulatory FoxP3+ T (Treg) cells, Th17+ cells, NK cells and senescence-associated CD28- T cells. Results: RA patients were more depressed than controls, but stress levels were similar in the 2 groups. Patients had impaired memory performance compared to controls, demonstrated by lower Mini-Mental State Examination scores and logical and working memories (all p < 0.0001). These group effects remained significant after correcting for depression and age. Patients had expansion of regulatory T cells, naïve CD4+ T cells and CD8+CD28- cells but reduced percentages of B cells and memory CD8+CD45RO+ T cells compared to controls. CD8+CD28- and CD8+CD45RO+ T cells were found to be negatively associated with memory. Conclusion: RA patients had reduced memory performance compared to healthy controls. Expansion of activated and senescence-associated T cells was correlated with poor memory performance.