North Korea poses fewer health risks than its southern neighbour. Not being a tropical country, it has no hosts of mosquitoes to give you malaria or dengue fever; no stagnant pools of monsoon water to cause typhoid, and on the whole, a drier, cooler and less polluted atmosphere. There is some risk of rabies and cholera, so you should get vaccinations beforehand. Other than this, there is not much risk of serious illness, but be prepared not to get western medicine should you fall ill. There are few western medical practioners to be found outside large cities like Pyongyang, Haeju and Kaesong. There are medical systems, of course, but these are of Korean medicine- based on herbs and various plant and animal products (some of very dubious origin!). Korean traditional medicine is similar to Chinese medicine in some ways. In the light of this, it makes sense to get yourself medically insured before you set off for North Korea.
North Korea is relatively safe to travel in, at least as far as crime is concerned- although there have been recent incidents of petty theft especially in and around Pyongyang’s International Airport, street crime is fairly low. Simple precautions, such as keeping a hold on your bag or wallet, particularly when moving through crowded areas, not flashing your money around, and always keeping your valuables locked, will suffice.