In late summer 2016 cankers and shoot dieback were detected on a sweet chestnut (Castanea sativa) tree (Figs. 1-2) during a survey for chestnut blight (Cryphonectria parastica) in southeast England. The tree was part of a two-year-old amenity planting scheme. Samples of the affected shoots were sent to the Tree Health Diagnostic and Advisory Service at Forest Research for examination. Isolations were made from the margin of the lesion and plated onto malt agar amended with 1% streptomycin, and the plates incubated for 4 days at 20°C in the dark. A fungus grew consistently from the affected tissues and growing colonies were transferred to 2% potato dextrose agar (PDA) and incubated further. The fungus formed a white fluffy colony on PDA after seven days (Fig. 3) and readily produced hyaline, fusoid, obovoid and multi-gutulate conidia which were straight or slightly curved (without appendages) after 14 days. Spore dimensions were 5-7.5 μm x 1.25-2.5 μm. DNA was extracted from mycelium and the ITS region was amplified and sequenced with the primers ITS1 and ITS4. Based on morphological features and ITS sequences the identity of the fungus was confirmed as Gnomoniopsis smithogilvyi (Shuttleworth et al., 3). The sequences of the ITS showed 100% identity with sequences of G. smithogilvyi deposited in GenBank and a representative sequence was submitted to GenBank (Accession No. KY695232).