A new global report says HIV infections are rising in about 50 countries.
The report, launched by UNAids, says half of the people who are newly infected with the virus are not receiving the treatment they need to prolong their lives.
Nearly 37 million people across the world are living with the virus that causes Aids.
The syndrome kills about one million people each year.
UNAids is warning that progress towards controlling the spread of HIV is slowing globally.
However, the region worst hit by the infection – East and southern Africa – recorded the biggest drop in new infections.
This is because there is much more awareness and the majority of people living with HIV use life-prolonging medication.
The drugs also help to reduce the spread of HIV.
West and Central Africa, however, lag behind; three quarters of children and three out of five adults who need treatment are not receiving it.
The report notes that Nigeria, in particular, has made very little progress, even though it has high rates of HIV infection.
Stigma and discrimination against people living with HIV remains high in most countries.
In some, as many as half of the people interviewed said they didn’t think children with HIV should attend the same schools as those without the virus.