Lower back pain is prevalent in equestrian athletes, but its prevalence and associated factors are unknown in the Portuguese equestrian population. A questionnaire regarding lower back pain and possible associated factors was answered by 347 respondents. Of the respondents, 214 (61.7%) stated having experienced lower back pain in the past 12 months and therefore completed the Roland Morris disability questionnaire. Among the latter, 63.1% stated that lower back pain impaired their performance. The probability of suffering from lower back pain was higher in individuals with higher weekly riding workloads, who reported equestrianism as their main occupation, and who performed daily stable duties. Considering a Roland Morris disability score of 4 as the cut-off value for dysfunction, this sample had an average score of 5.39 ± 4.42. Individuals who stated equestrianism was their main occupation showed a significantly higher risk (OR = 1.759, p = 0.041) of exhibiting a score ≥ 4 than those who stated equestrianism as a hobby. Age (p = 0.029), body mass index (p = 0.047), and daily performance of stable duties (p = 0.030) were also associated with a higher Roland Morris disability score. Further research is needed to understand the full impacts of lower back pain in Portuguese equestrian athletes.