Few studies have comprehensively addressed the association of social factors and elements of pre-end-stage renal disease (ESRD) care with the selection of dialysis modality. This study examines the relative contribution of demographic, medical, social, pre-ESRD, and geographic factors to modality assignment among new ESRD patients. Data were collected from the Dialysis Mortality and Morbidity Wave 2 Study, a national random sample of 4025 patients in 1996 and 1997. In multivariate analyses, the selection of peritoneal dialysis (PD) over hemodialysis (HD) was significantly associated with younger age, white race, fewer comorbid conditions, and lower serum albumin. Greater use of PD was seen in patients who were employed, married, and living with someone before the start of ESRD and in those who were more autonomous and more accomplished educationally. Patients referred earlier to a nephrologist (> 4 mo versus < or =4 mo) and seen more frequently by a nephrologist (> or =2 visits versus < 2 visits) in the pre-ESRD period had greater PD use. Of the factors listed, 25% of the variability (R(2)) in PD use was explained by demographic (4.1%), comorbid (1.2%), social/pre-ESRD (14.5%), and geographic (5.2%) factors. This study identifies several clinical, social, and pre-ESRD factors with the selection of PD, and it underscores the importance of patient education, autonomy, and a strong social support system in improving rates of PD use in the United States. As pre-ESRD patient care is an important contributor to PD use in the United States, greater efforts should be expended in improving its delivery earlier in the pre-ESRD period.