This paper compares the characteristics of those experiencing short spells of low income with those having longer spells. Data from the 1984 panel of the Survey of Income and Program Participation (SIPP) was examined. It was found that short spells--less than six months--are quite common, and make up a substantial proportion of all poverty spells. About 30 percent of the population as a whole has at least one month with an income of less than the poverty level (adjusted to a monthly basis) over an observable period of 16 months. About half of those entering poverty leave within the first three months, and about 80 percent leave within six months. The probability of leaving poverty was highly related to the probability that someone in the family would begin earning again in the near future. Specifically, families with a member who had recently become unemployed were particularly likely to leave poverty quickly, since most unemployed persons with previous earnings find re-employment fairly rapidly. Conversely, those who were less likely to have earnings in the recent past--female-headed families (especially with children) and the elderly--were more likely to have longer spells of poverty. Those seen to be poor on a cross-sectional basis contained a larger proportion of longer-spell cases than did the cohort of poverty entrants, although even those poor on a cross-sectional basis were in the midst of a spell that lasted less than six months. Age and racial differences in poverty duration are discussed. Data are presented on nine tables. A list of references is included. (BJV)