In the author’s opinion, the possibility of the private detective, performing a contract of mandate, processing a special category of personal data, the so-called sensitive data is an important issue because such activity interferes with the civil rights and freedoms granted by the Constitution of the Republic of Poland, in particular the right to privacy and the right to protect one’s personal data. Moreover, if this right does get granted, this has a practical dimension as well, because it can apply to many categories of cases, especially family cases, and nowadays there is an increased interest in the services provided by private detectives. It is worthwhile to pay attention to this issue, and the signpost outlining the direction of these considerations is Article 31(3) of the Polish Constitution.