Being a tropical country, Laos is prey to most of the diseases common in the tropics- hepatitis, polio, malaria, dengue, typhoid, diptheria and tetanus. Although there are no mandatory vaccinations required (other than yellow fever, if you’re coming from an infected zone), it makes sense to get vaccinations against some or all of these diseases, particularly if you’re travelling to Laos during the summer or monsoons, or will be spending a lot of time in rural areas. Whatever the case may be, while in the country, it’s wise to take precautions- drink only boiled or bottled water, eat food (wherever possible) which is freshly cooked and hot, and guard against mosquitoes- insect repellant, malaria pills, trousers and long-sleeved shirts are a good idea.
Medical facilities in Laos are fairly limited, except in Vientiane (where they are, at the most, just about adequate). Carry along any medication you’re likely to need, and, if possible, a basic first aid kit.
Laos is a fairly safe country to travel in- street crime, including violent crime and petty theft- is relatively uncommon, and you need take only the basic precautions. Keep your valuables locked away, and don’t flash your cash about. When moving around in crowded areas, keep your bag or wallet in sight and close to you at all times.