Like any big city, San Jose has its issues with crime. However, most crimes are limited to petty offences, such as pickpocketing, or other theft. As with any locale you are unfamiliar with, it pays to be alert while traveling within large crowds, especially during the high season. Pickpockets can quickly pick you clean of your money or passport, quickly turning a dream vacation into a nightmare. Make use of your hotel's safe to protect items such as any jewelry you might have brought with you (which, in reality, is best left at home), extra monies, credit cards, and passports. Keep an eye (and hand) on bags at all times, and do not leave your items unattended.

In addition, when traveling abroad, it is often easiest to travel with traveller checques, which are easier to replace than cash or credit cards if stolen. Keep a copy of the front page from your passport, any tickets, traveller checque serial numbers, and any other important information in a location separate from the originals. These will come in handy if you are a victim of theft.  

Locations where you should take extra care include the area surrounding La Coca-Cola domestic bus terminal. Since taxis are very common and cheap, it just makes sense to take a taxi to the bus terminal, rather than schlepping yourself and your belongings there, and sticking out like the tourist that you are.

In addition, be aware that drivers in San Jose are extremely aggressive, and pedestrian right-of-way is a foreign concept. Just like you learned when you were five, look both ways before crossing the street. Don't think that vehicles will stop for you; just like a game of frogger, the vehicles will keep coming in your direction.