Waarnemingen.be - Butterfly occurrences in Flanders and the Brussels Capital Region, Belgium is a species occurrence dataset published by Natuurpunt and described (v1.4) in Maes et al. (2016, https://doi.org/10.3897/zookeys.585.8019). The dataset contains close to 1.3 million butterfly (Lepidoptera excluding moths) occurrences of 69 naturally occurring species (native, vagrant or migrant species), recorded by volunteers (citizen scientists), mainly since 2008. Together with the dataset Maes et al. (2016, https://doi.org/10.15468/njgbmh), it represents the most complete overview of butterflies in Flanders and the Brussels Capital Region (north Belgium). The occurrences are derived from the database http://www.waarnemingen.be, hosted at the nature conservation NGO Natuurpunt in collaboration with Stichting Natuurinformatie. Standardized information regarding the occurrence's sex, lifeStage, behavior, occurrenceRemarks, and samplingProtocol is included as well. Generalized and/or withheld information: location information is generalized to 5 x 5 km² Universal Transverse Mercator (UTM) grid cells. Observer name, exact XY-coordinates, toponyms, and photographs are not included in the published dataset, but are known in the source database. To allow anyone to use this dataset, we have released the data to the public domain under a Creative Commons Zero waiver (http://creativecommons.org/publicdomain/zero/1.0/). We would appreciate however, if you read and follow these norms for data use (http://www.natuurpunt.be/normen-voor-datagebruik) and provide a link to the original dataset (https://doi.org/10.15468/ezfbee) whenever possible. If you use these data for a scientific paper, please cite the dataset following the applicable citation norms and/or consider us for co-authorship. We are always interested to provide more information or know how you have used the data, so please contact us via the contact information provided in the metadata or natuurdata@natuurpunt.be. The publication of this dataset is supported by INBO and funded by Research Foundation - Flanders (FWO) as part of the Belgian contribution to LifeWatch.