In 2007, prevalence of root rot pathogens and disease yield losses were studied under prevailing environmental conditions in common bean fields at Zanjan. Root rot disease incidence varied by sampling time and location of a field. In the majority of fields, Fusarium solani was the predominant fungus, being isolated from 2.8 to 96% of root samples over the sampling time, followed by Rhizoctonia solani, Macrophomina phaseolina and F. oxysporum. At pod maturity, the mean values for investigated factors were: disease incidence, 4.7–95%; disease severity, 0.1–2; disease index, 0.1–29%; number of seeds, 3.3–19; number of pods per plant, 8.3–62; and 100-seed weight, 19–53 g. Regression analysis demonstrated that disease incidence, disease severity and disease index were negatively correlated with both the number of pods or seeds per bean plant, whereas there was a positive correlation between the disease and 100-seed weight. If the indicative relations obtained between the disease and yield components are confirmed by further studies, then findings may contribute to the future estimation of bean yield losses to root rots and selection for resistant cultivars.