If you are staying less than 4 months but need to arrange any affairs with Dutch government agencies, you will need a Citizen Service Number (BSN). This can be obtained by registering as a non-citizen (RNI).
If you are visiting the Netherlands from abroad to work or study and/or you will be staying less than 4 months, you are not required to register as a resident. However, in the case that you must arrange any affairs with Dutch government agencies, you will still need a Citizen Service Number (Burgerservicenummer - BSN). This can be obtained by registering as a non-citizen (Register Niet- Ingezetenen - RNI). You do not need a Dutch address for RNI registration.
You should be aware that an RNI registration means you will have a BSN but you will not appear in the Personal Record Database (Basisregistratie Personen - BRP). This can make getting health insurance in the Netherlands very difficult. However, health insurance is only mandatory after 4 months of living in the country.
You can contact the Municipality of Leiden, or one of 18 other selected municipalities to make an appointment to do this. For an RNI registration appointment, you can select any of the 19 RNI desks available in the Netherlands, regardless of which one is closest to you. The RNI desks are located in: Alkmaar, Almelo, Amsterdam, Breda, Doetinchem, Eindhoven, Goes, Groningen, Heerlen, Leiden, Leeuwarden, Nijmegen, Rotterdam, Terneuzen, The Hague, Utrecht, Venlo, Westland, and Zwolle.
Registration as non-citizen is not offered at the LIC; you will need to call the Municipality of Leiden at +31 71 516 516 5, or one of the other municipalities mentioned above.
You will need to visit in person and present a valid proof of identity (a passport or identity card) and will be asked to provide your address outside of the Netherlands.