With sensible precautions and behaviour, the health risks to travellers in PNG are low. Mosquito-transmitted disease is the main problem.
The World Health Organization (WHO) recommends that all travellers be covered for diphtheria, tetanus, measles, mumps, rubella and polio, regardless of their destination.
Vaccination for yellow fever (and the certificate to prove it) is required if you are entering from a yellow fever–endemic country. Vaccinations are also recommended for hepatitis A, hepatitis B, typhoid fever and Japanese B encephalitis.
Malaria, both malignant (falciparum) and the less threatening but relapsing forms, are found in all areas of PNG below 1000m. Since no vaccine is available you’ll have to rely on mosquito-bite prevention (including exposing as little skin as possible, applying topical insect repellents, knockdown insecticides and, where necessary, bed nets impregnated with permethrin) and taking antimalarial drugs before, during and after risk exposure.
In Port Moresby and Lae you can expect primary care of a high standard but limited by the lack of access to sophisticated medical equipment. Specialists in internal medicine, surgery and obstetrics/gynaecology are also available in these centres, while in Port Moresby there are also paediatric, orthopaedic, dental and psychiatric specialists.
In secondary centres (eg Madang), the quality of service can be lower – often because of lower-quality diagnostic and treatment facilities. Small hospitals, health centres and clinics are well placed throughout these centres but staffing and facilities will vary.
The municipal water supply in the capital and in the majority of major towns can be trusted. If you’re trekking, drink only from streams at a higher altitude than nearby villages. It's always a sensible precaution to boil, filter or chemically disinfect water.