— I/Q imbalance has been identified as one of the most serious concerns in the practical implementation of the direct conversion receiver architecture. Facing the performance-degrading impact of the I/Q imbalance, in particular at the reception of multi-carrier signals, various digital estimation and compensation techniques have been proposed in the literature. Knowledge about the quantitative link between the I/Q imbalance parameters, with or without digital compensation, and the resulting error probability is essential for both a reasonable design of the receiver front-end and for the dimensioning of the digital compensation algorithms. The objective of this paper is to quantify the impact of the I/Q imbalance in terms of closed-form error probability formulas, providing the desired theoretical link between cause and effect of the I/Q imbalance.