Technical Abstract: Stem diseases of blueberry (Vaccinium spp.) can cause significant crop loss as well as loss of entire bushes. Stem diseases also tend to be more difficult to control with fungicides than foliar or fruit diseases. A screening program was initiated to test blueberry cultivars for resistance to Botryosphaeria stem blight and Phomopsis twig blight. An attached stem assay was developed to compare the host response to both pathogenic fungi. Relative resistance was expressed as a comparison of stem lesion lengths on a log scale, taken at 4 weeks post-inoculation. Whole potted plants of 50 blueberry cultivars were used for the study. For Botryosphaeria stem blight, lesion length ranged from about 10 mm in resistant cultivars to about 140 mm in susceptible cultivars. The half-high cultivars Northsky, Northblue, Chippewa, and the low bush cultivar Putte were among the most resistant. Phomopsis twig blight lesions ranged in length from about 18 mm to 98 mm. Similar to results for Botryosphaeria stem blight, resistance was limited to half-high (‘Northsky’ and ‘Chippewa’), and lowbush (‘Blomidon’, ‘Chignecto’, and ‘Cumberland’) cultivars. Individual cultivars that expressed resistance to one pathogen were not necessarily resistant to the other, though the resistances were correlated. Ninety-five percent confidence intervals were established for all cultivars to predict performance across years. Although the cultivars tested varied in resistance, the largest single factor affecting lesion length was isolate strain. These data identify selections of cultivars for resistance to both diseases that can direct planting in problem areas as well as parental material for breeding cultivars with improved resistance.