All patients 65 years and older who had been living in an institution for at least six months had a measurement of red blood cell folate (RBCF), serum folate (SF), vitamin B12, hemoglobin, and mean corpuscular volume. Twenty-two percent of the 97 studied subjects were found deficient in RBCF, although only 6% had anemia. Length of stay at the institution was significantly associated with deficiency in RBCF and this association was uncon-founded by age. The proportion of RBCF deficiency among the studied subjects attributable to length of stay is 80%. The prophylactic administration of folate among long-term nursing home type of patients should be considered.