This paper analyses the determinants of the default ratio associated to banking debt in Spanish non financial firms over the period 1992-2003. It studies the factors influencing firms' entering and exit processes in and out from the default status. Additionally, it explores the factors explaining the relative amount of non performing banking debt in defaulted firms. The database combines firm-level data for non-financial companies drawn from two sources: SABI-INFORMA and Credit Register of Banco de Espana. The methodological approach is an application of Heckman's selection model. Results indicate that the decreasing trend in the evolution of the aggregate default ratio over the studied period is mainly attributable to the moderation in the level of the default ratios in those firms in which the default status is persistent over time. The contribution to the evolution of the aggregate default ratio of firms' turnover in a out from the default status has been fairly stable over time.