Vientiane is a fairly safe city in terms of crime. However, bag snatching from guests sitting in front of cafes is becoming more common. Bags in the baskets of rented bicycles or mopeds, even when moving along, are also far from safe. Do not leave a bag in an accessible position. If your bag is snatched, immediately start shouting: the perpetrators rely on tourists reacting by silently trying to chase them without alerting the numerous police boxes. The thieves are often drug addicts.
Probably a bigger hazard than crime is the missing sewer covers on sidewalks. Additionally, there are many loose sidewalk stones that will tip if stepped on. Tread carefully and exercise extreme caution at night.
To prevent the development of a sex trade industry, which is so prevalent in neighbouring Thailand, Laotian law bans foreigners from having sexual relations with Laotian nationals other than their spouses. This law is enforced by the village chief and, given the fines, the incentive to enforce is high. The penalty is US$500 for the first offense, though as the text of the law is not available, the fine could be much more the U.S. Embassy says US$5,000; the foreign offender can face prison or deportation and the Lao woman prison. A Laotian prison is the last place anyone would want to be. If you take a girl to your room and she robs you, this law makes it almost impossible to obtain police assistance. Foreign women should note that, while rare, Laotian police enforce this law on both sexes. Bartenders are happy to provide stories of angry tourists confronting girls at the same bars they picked up the night before. Most hotels also do not allow foreigners to take girls to their rooms as it is officially prohibited.
Homosexuality is legal and there is a fairly open gay scene in Vientiane. Since the Pathet Lao took over in 1975, the Lao government has been completely silent on LGBT rights and homosexuality itself. Female homosexuality is relatively frowned upon for Lao women while male homosexuality is widely tolerated. A growing acceptance of homosexuality in Laos continues. Gay and lesbian travelers should be aware though that some hotels will impose the same restrictions as for straight people and not allow a Lao national into your room.
Illegal drugs are a problem throughout Laos and certainly so in Vientiane where even very young children can try to peddle "happy pills" to tourists. After declaring victory in the "war on opium" in 2005, it is not so much opium and heroin these days as methamphetamine that incurs the wrath of the authorities. Penalties are extremely harsh, though those caught can probably bribe their way out of trouble.
As noted above, dogs - whether stray or just owned by irresponsible idiots - are dangerous, especially at night. Stay on well-lit, busy streets.
respect
Long trousers and sleeves are recommended when visiting a temple or official offices. Foreign women adopting the traditional long sarong siin are very appreciated.
dogs
They can be vicious, whether they're stray or just owned by irresponsible people who don't bother closing their gates. You don't need to be out in the suburbs to be attacked. Avoid anything but the most well-lit, busy streets at night.
If you're bitten see a doctor. Even if you've had a rabies vaccination before your trip: you will still need a booster jab.
water
The city's waterworks are called Nam PaPaa, which some may joke means "water without fishes". Yes, the fishes have been removed but not everything else. Don't drink the tap water, no matter how long it's been boiled it tastes very industrial - stick to the bottled water available everywhere, though even that varies in quality. Some people have a major preference for clear plastic bottles.
mosquito-borne diseases
Vientiane is free from malaria, but dengue is a real threat, especially during the rainy season. Take the necessary precautions against mosquito bites by wearing DEET repellent - available to purchase at any minimart. It is common practice to request a mosquito coil at dusk at outdoor venues.