The number of solo self-employed is increasing in many Western economies yet available government statistical data sources are not always well designed to assess the magnitude of this phenomenon and its modalities. This paper provides an overview of the most relevant public data sources, and discusses the pros and cons of each data source regarding the available data on solo self-employment and its various segments (e.g. freelancers, hybrid entrepreneurs, dependent entrepreneurs). We conclude that, at present, labour force surveys are superior to business establishments registers when it comes to researching solo self-employment. However, using data from the Polish statistical office, we also demonstrate the value added of combining both types of data sources.