Dalfampridine extended release tablets (D-ER; prolonged-release fampridine in Europe) are available to improve walking in patients with multiple sclerosis (MS). D-ER is mainly renally eliminated; the approved 10-mg twice daily dose is contraindicated in the United States in patients with moderate or severe renal impairment. This study evaluated single-dose and steady-state pharmacokinetics of a 7.5-mg dose of D-ER in healthy subjects (n = 13) and subjects with mild (n = 17) and moderate (n = 12) renal impairment. D-ER plasma concentrations were consistently higher in subjects with renal impairment relative to healthy individuals with a significant (P < .0001) inverse linear relationship between creatinine clearance and drug exposure. Steady-state AUC0–12 among healthy subjects, 167.0 ± 55.3 ng h/mL, increased 74% and 151% with mild and moderate renal impairment, respectively. The overall incidence of adverse events was 61.5%, 47.1%, and 33.3% in healthy subjects, and subjects with mild and moderate renal impairment, respectively, and for treatment-related adverse events the rates were 0%, 17.6%, and 8.3%, respectively. The most common adverse events were headache, dizziness, and arthralgia. The pharmacokinetics of D-ER 7.5-mg twice daily in subjects with mild renal impairment was comparable to 10-mg twice daily in patients with MS who had normal renal function. Exposure was significantly higher in moderate renal impairment.