Stay safe & healthy
Namibia is a peaceful country and is not involved in any wars. With the end of the Angolan civil war in May 2002, the violence that spilled over into northeastern Namibia is no longer an issue.
Namibia does, however, have a relatively high crime rate. Be careful around ATMs. For foreigners, it is not prudent to walk or ride taxis alone after sunset. Pickpockets can be a problem. No local will carry a bag while walking, and for thieves the bag is the token to make out who is a tourist and who isn't. Stuff all possessions into your trousers' pockets. Lately, there are many armed robberies reported. For home security, electric fences are installed in almost every house in Windhoek.
Most reported robberies take place just outside of the city centre. The police report that taxi drivers are often involved: they spot vulnerable tourists and coordinate by cell phoning the robbers. Take these warnings in context; if you are alert and take some common sense precautions, you should have no problems. Never be specific when asked where you stay; "in town" or "at some B&B" is sufficient for all good-faith conversations and doesn't disclose your intended route.
Travellers should have no problem visiting the townships, but do not visit the townships alone unless you are familiar with the area. If you have been travelling in Southern Africa for a few months, you probably know what you are doing.
Namibia has a serious problem with driving under the influence of alcohol. The problem is aggravated because most people consider it no problem. When driving or walking on weekend evenings, be especially alert.
The HIV infection rate in Namibia is about 25%.
Namibia's medical system is modern and capable of attending to whatever needs you may have. Staff are well trained and so HIV transmission in hospitals is not an issue. This applies to government and private hospitals alike, though line-ups are often shorter at private hospitals, and there have been cases of incorrect diagnosis in government hospitals.
The northern part of Namibia is in a malaria-risk zone, so consult a doctor before leaving, and take appropriate malaria precautions when travelling in these areas.
Namibia's water supply is usually safe to drink, except where labelled otherwise. Campsites next to rivers often get their water directly from the river, so do not drink it!
Having said all this, make sure you consult a physician specializing in health issues of Southern Africa, as well as things like the Centre for Disease Control web page. Make sure you satisfy yourself of the safety of anything you're getting into.