Just like in the original game, your Sim has several basic needs. These are:

* Hunger
* Comfort
* Hygiene
* Bladder
* Energy
* Fun
* Social
* Environment

The sims in Sims 2 do MUCH better than the originals at maintaining their own needs. It is so much more fun to play when you aren't having to remind your sim to pee! It is important to keep an eye on the needs though, and give your sim a prod if he/she seems to be distracted by something shiny :)

The Sims 2 Tips, Techniques and Walkthroughs