Background Gait deviations are often seen in adults with intellectual disabilities (ID). Their low physical fitness levels may be associated with these deviations. Understanding the impact of fitness on gait in this population is important for developing interventions to improve gait. In a cross-sectional study, we assessed the association between multiple physical fitness components and spatiotemporal gait parameters in adults with ID. Method Gait characteristics of 31 adults (42.77 ± 16.70 years) with ID without Down syndrome were assessed with the GAITRite at comfortable (CS) and fast speed (FS), along with fitness assessments (body composition, muscular endurance, strength, balance, Short Physical Performance Battery). Results At CS, adults with ID with higher BMI and/or waist circumference spent more time in double support. At FS, those with better muscular endurance took steps faster, those with better balance took bigger steps and strides and those with better Short Physical Performance Battery scores took bigger steps and strides at higher velocity. Conclusions Body composition was mostly associated with gait at CS, while the other physical fitness