Purpose: Side effects of chemotherapy on cognitive functions in older patients have rarely been investigated. Addressing this lack of research, the present study evaluated cognitive functions in older cancer patients. Methods: A total of 130 younger (n=59; age<60) and older (n=71; age≥60) cancer patients with hematological disease or cancer of the intestinal tract took part in the study. To explore short-term effects of chemotherapy, a group of patients assessed before the start of chemotherapy was compared with patients who already received their first course of chemotherapy. Results: Cognitive impairments of verbal learning, word fluency, and memory were observed following the first few days after treatment onset. Older patients showed stronger memory impairments after start of chemotherapy than younger cancer patients. Additionally, depression was neither associated with short-term effect of chemotherapy nor with age. Conclusions: The results suggest that chemotherapy has negative short-term effects on some cognitive functions. But age-dependent effects were only found for memory.