Epidemiological studies on the potential health effects of dietary polyamines are scarce. The present study aimed to estimate habitual intake of polyamines (putrescine, spermidine and spermine) and examine whether spermidine intake is inversely associated with all-cause and cause-specific mortality in a population-based cohort study in Japan. The study included 13 355 men and 15 724 women aged 35 years and older. Diet was assessed via a validated FFQ at the baseline in 1992. The intake of polyamines was estimated mainly using databases of polyamine content in foods consumed among Japanese population. Sex-specific hazard ratios (HR) and 95 % CI for all-cause and cause-specific mortality were estimated according to polyamine quartiles. During 16 years of follow-up, 2901 deaths in men and 2438 in women occurred. The intake of any polyamine was not significantly associated with all-cause or cause-specific mortality after controlling for covariates in men and women. There was a suggestive positive association between spermidine intake and cancer mortality in women: HR for the highest v. lowest quartile were 1·38 (95 % CI (0·99, 1·93); Ptrend = 0·02). Our results did not provide support for the notion that dietary spermidine has beneficial effects on mortality. Further studies on dietary polyamines and longevity, as well as the morbidity of specific diseases, including cancer, are needed across populations with different dietary habits.