Aim: This study aimed to investigate the associations between health behavior adherence and psychological factors during the COVID-19 pandemic, with a particular focus on identifying trajectories of handwashing, mask wearing, social contact limitations, and physical distancing. Methods: We employed a multi-trajectory group-based approach to analyze data from 6026 Belgian residents, including 60% women, with an average age of 52.65. Data were collected over six waves spanning from April 2021 to December 2021. Results: Participants were categorized into trajectory groups based on persistently low (11.9%), moderate-low (20.9%), moderate-high (39.1%), and high (28.1%) levels of adherence to the specified health behaviors. Our findings indicate a declining trend in health behavior adherence over the study period. Additionally, we observed that females, older individuals, and those with prior COVID-19 infection had a higher likelihood of belonging to trajectory groups characterized by the highest levels of health behavior adherence. Similarly, individuals with positive vaccination intentions, a heightened perception of consequences, and increased health anxiety demonstrated greater adherence to health behaviors over time. Furthermore, our investigation into the relationship between health behaviors and mental health revealed that participants in trajectory groups with higher levels of adherence to social contact limitations and physical distancing reported increased feelings of loneliness and decreased life satisfaction. Conclusions: The COVID-19 pandemic has reshaped our lives, and while vaccines have marked progress, maintaining health behaviors is crucial for virus prevention. To address potential mental health challenges from sanitary measures, policies and communication should promote health behaviors while acknowledging their psychological impact