The European hazelnut (Corylus avellana) is an important fruit crop cultivated in Chile, with more than 17,000 ha planted (46%) in the Maule region, central Chile. During a routine orchard survey in seasons 2020 to 2021 and 2021 to 2022, in the Maule region, canker and dieback symptoms were observed in two commercial orchards of European hazelnut cultivar Tonda Di Giffoni in San Rafael (8-year-old trees) and Linares (15-year-old trees), with an incidence of 10 and 36%, respectively, based on external symptoms. Twenty symptomatic branches exhibiting cankers, reduced vigor, wilting, twig death, and dieback were collected. A cross-section of diseased branches revealed mostly brown V- or U-shaped cankers of hard consistency. Branches were cut, and pieces of cankers were surface-sterilized in 96% ethanol for 3 s and briefly flamed. Small pieces of wood (5 mm2) from the edge of the cankered tissues were placed on potato dextrose agar (2% PDA) amended with 0.1% Igepal CO-630 and incubated at 25°C for 5 days in the dark (Díaz and Latorre 2014). Pure cultures were obtained by transferring a hyphal tip from growing colonies to fresh PDA media. Eight pure cultures (NP-Haz01 to NP-Haz08) developed dark to olive-brown fast-growing colonies with scarce aerial mycelium after seven days at 25°C on PDA under near-UV light. These isolates showed a dark-olive color on the reverse side of Petri dishes and developed abundant, aggregated, and dark-brown globose pycnidia after 21 days at 25°C. Conidia were hyaline, aseptate, ellipsoidal, densely granulate, externally smooth, thin-walled, and dark and measured (9.5–) 15.5 ± 1.2 (−17.3) × (5.1–) 7.2 ± 0.6 (−9.1) μm (n = 30), with a length/width ratio of 2.15. These isolates were tentatively and morphologically identified as Neofusicoccum sp. Molecular identification was performed using ITS1/ITS4, Bt2a/Bt2b, and EF1-728F/EF1-986R primers of the internal transcribed spacer (ITS1-5.8S-ITS2) region, a portion of the beta-tubulin (BT), and part of the translation elongation factor (EF1-α) genes, respectively (Dissanayake et al. 2015). A MegaBLAST search in GenBank showed a 99% similarity to the isolate CMW9081, the ex-type of Neofusicocum parvum (Pennycook & Samuels) Crous, Slippers & A.J.L. Phillips. The sequences were deposited in GenBank (OR393855 to OR393857 for ITS; OR400688 to OR400690 for BT; and OR400691 to OR400693 for EF1-α). Pathogenicity of three isolates (NP-Haz02, NP-Haz04, and NP-Haz09) was studied on fresh pruning wounds of attached branches of 3-year-old and 1-year-old trees of European hazelnut cultivar Tonda Di Giffoni in the San Rafael field. Fifteen pruning wounds were inoculated with 40 μl of conidial suspension (105 conidia/ml) of each isolate of N. parvum. Sterile distilled water was used as a control treatment (n = 15 branches) for branches of 3-year-old trees and 1-year-old trees. Both pathogenicity tests were repeated once. Attached branches of 3-year-old trees (6 months of incubation) and 1-year-old trees (4 months of incubation) developed necrotic streaks and cankers with a mean length of 33 to 82 mm and 25 to 51 mm, respectively. No necrotic streaks were observed in the branches treated with water. N. parvum was reisolated only from symptomatic tissues of inoculated branches, and it was morphologically and molecularly (EF1-α) identified, thus fulfilling Koch’s postulates. Previously, other Botryosphaeriaceae species, such as Diplodia coryli (Guerrero and Pérez 2013) and D. mutila (Moya-Elizondo et al. 2023), have been obtained from canker and dieback of hazelnut in Chile. Recently, N. parvum was reported causing nut rot in hazelnuts in Italy (Wagas et al. 2022). To our knowledge, this is the first report of N. parvum causing canker and branch dieback in hazelnut trees in Chile and worldwide.