Sexually transmitted infections (STIs) remain a public health challenge in Brazil, with increasing incidence among young people. It is estimated that 25% of all cases occur in individuals under 25 years old. Condom use remains the most effective prevention method in this population.

To describe condom use and reasons for nonuse among young adults attending a Counseling and Testing Center (CTA).

Cross-sectional study conducted at a CTA in Northern Minas Gerais. All individuals aged 18 to 29 years who attended between January and November 2024 were included. Data were extracted from counseling and testing forms and analyzed descriptively using absolute and relative frequencies. Ethical principles were followed, and the study was approved by the Research Ethics Committee.

The sample comprised 563 young adults, 39.1% aged 18–23 years and 60.9% aged 24–29 years; most were male (73.5%), single (86.7%), and had more than eight years of education (84.4%). Regarding substance use, 63.3% reported alcohol consumption and 20% other drugs. Among those with a steady partner in the past year, 84.4% reported having only one partner, and 80% did not use condoms regularly. Among those with casual partners, 29% reported more than five partners, and 57.7% did not use condoms or used them inconsistently. The main reason for nonuse was trust in the partner, reported by 88% in steady relationships and 59.8% in casual ones. Other reasons included dislike of condoms and alcohol/drug use.

Condom use was low, even in casual relationships typically associated with higher risk. Trust in the partner, both in steady and casual relationships, was the main reason for nonuse, followed by aversion to condoms and psychoactive substance use. Additional contributing factors include low personal risk perception, gender power inequalities, easier sexual encounters facilitated by social media, and the normalization of HIV infection due to therapeutic advances. These findings reinforce the need for continuous educational strategies within both health and educational settings.