The purpose of this study was to examine the relationship between common laboratory values and cognitive functioning among 129 inpatients referred for neuropsychological evaluation. Laboratory values were recorded at admission, at the time point closest to neuropsychological evaluation, and at the time of peak metabolic derangement. Cognitive status was evaluated with the modified Mini-Mental State Exam. Patients with hyperglycemia, hypochloremia, and/or elevated creatinine at admission exhibited cognitive deficits. Patients with hyperglycemia, hyperchloremia, hypernatremia, hyperkalemia, leukocytosis, low hemoglobin, elevated blood urea nitrogen, and/or elevated creatinine at the time of peak metabolic derangement exhibited cognitive deficits. Different lab abnormalities at the time of peak metabolic derangement accounted for unique patterns of neuropsychological impairment. Lab values drawn at the time point closest to neuropsychological evaluation were not significantly associated with cognitive functioning. Results support and quantify common clinical beliefs that metabolic abnormalities are associated with global cognitive changes among elderly inpatients.