Within Warsaw, a car is more of a liability than a convenience. Traffic jams are frequent and parking problematic, with a significant threat of theft—of contents, parts, or the entire car—if you leave a Western model unattended. If you do bring your car, park it overnight in a guarded parking garage.
A car can be a useful independent means of transportation if you are planning to travel around Mazovia to explore the countryside and off-the-beaten-track sights. For example, you may wish to follow the route from Warsaw to Łódź via Żelazowa Wola, Arkadia, Niebórow, Łowicz, and Tum.
Major international car-rental agencies have offices in both Warsaw's and Łódź's city center and at the airports as well.