Butterfly monitoring scheme in Flanders, Belgium is a sampling event dataset published by the Research Institute of Nature and Forest (INBO). This dataset contains transect data for butterfly species, collected using a standardized protocol since 1991. Data from 1991-2014 were collected in the INBO Vlinderdatabank (Maes et al. 2016), but have since been migrated to the meetnetten.be database, where new observations are recorded. Here, the dataset is published as a standardized Darwin Core Archive and includes for each sampling event an eventID, date, location and sampling protocol (in the event core), the cloudiness, temperature, and wind force at the time of the event (in the measurement or fact extension) and for each occurrence an occurrenceID, the number of recorded individuals in a transect, lifestage, status (present/absent), vernacular and scientific name (in the occurrence extension). Issues with the dataset can be reported at https://github.com/inbo/meetnetten-occurrences/issues Generalized and/or withheld information: location information is generalized to 5 Universal Transverse Mercator (UTM) grid cells. Original locations are available upon request. We have released this dataset to the public domain under a Creative Commons Zero waiver. We would appreciate it if you follow the INBO norms for data use (https://www.inbo.be/en/norms-data-use) when using the data. If you have any questions regarding this dataset, don't hesitate to contact us via the contact information provided in the metadata or via opendata@inbo.be.