We provide the first available statistics on the extent to which successive birth cohorts have entered Social Security Disability Insurance (SSDI), and on cross-cohort trends in the average number of years of SSDI benefit receipt among all individuals of a given birth cohort. Following cohorts born from 1955 to 1974, we find that the percentage of each birth cohort entering SSDI by a given age generally increased for both men and women, with some slowing of that growth in more recent years. Mean years of benefit receipt by a given age among all individuals in the birth cohort grew more rapidly, due to the combined effects of increased entry before that age and lower mortality after entry. For cohorts born in 1955 to 1964, mean years of benefit receipt by age 50 increased by 18 percent for men (0.54 to 0.64 years) and by 50 percent for women (0.38 to 0.57 years). These findings largely hold when we account for immigration, which is important because cross-cohorts trends in immigration may be masking important cross-cohort trends in SSDI entry.