The present work describes the individual, selective and simultaneous quantification of acetaminophen (ACP) and tramadol hydrochloride (TRA) using a modification-free boron-doped diamond (BDD) electrode. Cyclic voltammetric measurements revealed that the profile of the binary mixtures of ACP and TRA were manifested by two irreversible oxidation peaks at about +1.04 V (for ACP) and +1.61 V (for TRA) in Britton-Robinson (BR) buffer pH 3.0. TRA oxidation peak was significantly improved in the presence of anionic surfactant, sodium dodecyl sulfate (SDS), while ACP signal did not change. By employing square-wave stripping mode in BR buffer pH 3.0 containing 8x10(-4) mol L-1 SDS after 30 s accumulation under open-circuit voltage, the BDD electrode could be used for quantification of ACP and TRA simultaneously in the ranges 1.0-70 mu g mL(-1) (6.6x10(-6)-4.6x10(-4) mol L-1) and 1.0-70 mu g mL(-1) (3.3x10(-6)-2.3x10(-4) mol L-1), with detection limits of 0.11 mu g mL(-1) (7.3x10(-7) mol L-1) and 0.13 mu g mL(-1) (4.3x10(-7) mol L-1), respectively. The practical applicability of the proposed approach was tested for the individual and simultaneous quantification of ACP and/or TRA in the pharmaceutical dosage forms.