Background <p>Thrombocytopenia (TP) has been associated with poor clinical outcomes in geriatric patients in the intensive care unit (ICU). However, the factors leading to TP in critically ill older patients are not clear. In this study, we aimed to investigate the primary factors influencing TP in geriatric patients in the ICU, as well as to evaluate the relationship between TP and adverse clinical outcomes.</p> Methods <p>Between 2010 and 2020, 5,848 geriatric patients were initially admitted to the ICU at Dongyang People's Hospital, with 3,147 ultimately included in the study. Lasso regression was used to screen for relevant variables, followed by multivariate logistic regression analysis. Propensity score matching (PSM) was used to further assess the impact of TP on in-hospital mortality. Validation of findings was conducted using the Medical Information Mart for Intensive Care database.</p> Results <p>32.6% of geriatric ICU patients developed TP during their stay. Compared with the non-TP group, the TP group showed significant increases in disease severity, hormone use, vasoactive drug use, and sepsis rates, as well as in-hospital mortality, mechanical ventilation use, duration of ICU stay, and hospitalization costs (<i>p</i> &lt; 0.001). Lasso regression screening identified 24 relevant variables, and 32.6% of patients developed TP during their ICU stay. Sensitivity analyses and PSM confirmed a strong association between TP and increased in-hospital mortality.</p> Conclusions <p>TP is common among geriatric patients in ICU and is associated with poor prognosis. This study identified several important factors influencing TP, highlighting valuable implications for the early identification of high-risk patients and the development of individualized treatment strategies.</p>