Clinical outcome of kidney grafts that are affected by the complex syndrome of 'early graft dysfunction' is uncertain and rather unpredictable. In this study, an individual prognosis for dysfunctioning allografts (N = 93) is attempted by the immunohistological assessment of vascular classical complement activation in graft biopsies. Thus, capillary deposition of complement fragment C4d was observed in the majority (N = 51) of early dysfunctioning grafts. In 43 biopsies, abundant deposition of fragment C4d was present in all capillaries, whereas in eight specimens a segmental distribution of capillary C4d was observed. In 42 grafts with early dysfunction no capillary C4d was detectable. Eighteen subsequent graft losses within one year (16 early losses) were recorded in the subgroup with C4d in all capillaries, and three early losses in the group with segmentally distributed C4d. Only four graft losses (3 early losses) were recorded in the C4d-negative group (P = 0.0027; Pearson's chi square test). The resulting one-year graft survival rates (72% for the study group) differed markedly between the subgroups. Grafts with generalized or segmental capillary deposition of C4d had 57% and 63% survival, respectively, contrasted by 90% survival in the C4d-negative group. It is of note, however, that also three of the four grafts that were finally lost within the C4d-negative group, showed distinct capillary deposition of C4d in second biopsies. Vascular deposition of complement fragment C4d therefore represents a clinically relevant factor that contributes to early graft dysfunction. Its assessment is helpful for an individual graft prognosis.