Recent data suggest that nonlinear GFR trajectories are common among patients with CKD, but the modifiable risk factors underlying these changes in CKD progression rate are unknown. Analyses relating baseline risk factors to subsequent GFR decline are suboptimal because these relationships often attenuate as follow-up time increases and these analyses do not account for temporal changes in risk factors. We identified 74 participants in the African American Study of Kidney Disease and Hypertension who had both a period of rapid GFR decline and an extended period of stability during a follow-up period of ≥12 years. We performed a within-patient comparison of time-varying risk factors measured during the periods of GFR decline and stability and identified several risk factors associated with faster GFR decline: more hospitalization episodes and hospitalization days per year; higher BP, serum phosphorus, and urine protein-to-creatinine ratio; lower serum albumin and urine sodium-to-potassium ratio; slower rate of decline of serum urea nitrogen, serum creatinine, serum uric acid, and serum phosphorus; and faster rate of decline of serum hematocrit and serum bicarbonate. By allowing each patient to serve as his or her own control, this novel, within-patient analytic approach holds considerable promise as a means to identify time-varying risk factors associated with stabilization of GFR or acceleration of GFR decline. Copyright © 2014 by the American Society of Nephrology.