Number line estimation (i.e., indicating the spatial position on a number line from which only start and endpoint are given) has been argued to measure the spatial representation of number magnitude aka the mental number line. However, recent evidence suggested that it draws heavily on visuo-spatial processes. In the present study, we evaluated influences of the latter on number line estimation by considering a sample of patients with neglect, a pathology which is known to specifically impair spatial processing. Therefore, we administered different tasks involving horizontal lines to neglect patients that showed a line bisection bias (NLB+) and compared their performance to i) neglect patients not showing a line bisection bias, ii) patients with right hemisphere damage without neglect, and iii) healthy controls. In a first task, participants had to segment a line into three or four equal parts. Results indicated that patients with a line bisection bias overestimated the size of lefthand segments. However, when lines were introduced as number lines (ranging from 0 to 10, requiring estimation of numbers 1, 4, 5, 6, and 9) NLB+ patients showed rightward overestimation for the numbers 4 and 5 compared to healthy controls. Additionally, all patient groups tended to place number 1 too far to the left and number 9 too far to the right, suggesting a bias towards endpoints. Our results support the notion that number line estimation draws on visuo-spatial processes (typically in terms of proportional reasoning) rather than reflecting a measure of the spatial representation of number magnitude.