The aim of the present study was primarily to investigate if periodontal healing assessed by reduction in probing depth over time is significantly influenced by the initial degree of horizontal radiographic attachment loss and secondly to what degree any such relationship influenced the already established correlation between presence of a root canal infection and impaired marginal healing. The investigation was conducted as a retrospective study on 160 patients referred to a specialist periodontal clinic. The choice of variables was guided by an assumption that each variable either positively or negatively contributed to determine probing depth reduction. It was found that healing after scaling and root planing over time was significantly impaired with more advanced loss of radiographic attachment. Regardless of the extent of radiographic attachment loss, healing after scaling and root planing was also significantly impaired over time by the presence of a root canal infection.