Dwarf mistletoes are parasitic flowering plants that infect conifers, resulting in substantial loss of growth and mortality. Recently, forest managers in Iran are contemplating whether infection of Juniperus polycarpos C. Koch forests by dwarf mistletoe, Arceuthobium oxycedri (DC.) M. Bieb, influences tree vigor and contributes to insufficient natural regeneration. The present study aimed at assessing the severity of infection and its impact on growth and reproductive output of J. polycar-pos. Infected and uninfected trees (n=20 each) were selected for assess-ment of diameter, height, crown area, and crown volume as well as quantity and quality of cones and seeds. The severity of infection of trees was determined by Hawksworth’s 6-class dwarf mistletoe rating (DMR) system. The DMR system revealed that 40%of the infected sample trees were lightly infected (DMR =1-2) and 60% were moderately infected (DMR =3-4). Growth characteristics did not differ significantly (p >0.05) between infected and uninfected trees. However, moderate infec-tion affected the reproductive output of J. polycarpos by significantly (p