Patients and staff members remembered those who died of the disease by placing commemorative ornaments on a Christmas tree.
But they also talked about saving lives and preventing infection.
In Houston, about three people are newly infected every day.
African Americans and men who have sex with men are the most severely affected.
But Congresswoman Sheila Jackson Lee says we also need to remember other groups:
Staff members at the Thomas Street Health Clinic in Houston decorate a "Tree of Remembrance" for World AIDS Day.
“There are populations that range from Asian to Hispanic to elderly, because the cultural stigma of expressing that you have something is very difficult. And I might also say for very religious communities of all races. And so we have mountains to climb and valleys to traverse.”
Staff member Bernie Vazquez started a support group at Thomas Street for Latinos who are HIV positive.
“A lot of people are always afraid thinking if they find out they have HIV, they’re going to lose their citizenship. So we noticed that it makes a lot of Latino not coming to get tested.”
The Harris County Health System treats more than 5,000 HIV/AIDS patients a year, enrolling many of them in research studies or clinical trials.
In addition, there is universal HIV testing offered in the county hospital emergency rooms and in the jail.
Almost 28,000 people have HIV or AIDS in Harris County.