To estimate the prevalence of pickup trucks transporting people in the cargo area and to identify factors associated to this behavior in three Mexican cities. Eight rounds of roadside observations of randomly selected pickup trucks were conducted from August 2012 to November 2014 in three Mexican cities: Guadalajara-Zapopan, León and Cuernavaca. Overall, 4.03% of the 4,611 pickup trucks observed were transporting people in the cargo area (95% CI: 3.48 - 4.64%). This implies that a total of 427 passengers were traveling unsafely in the cargo area of pickup trucks; of all them 22.01% were children and 82.20% were male. Prevalence of exposure to this risky behavior was higher in León (5.77%, 95% CI: 4.73 - 6.97%) than in Cuernavaca (3.73%, 95% CI: 2.49 - 5.35%) and Guadalajara-Zapopan (2.70%, 95% CI: 2.05 - 3.48%). According to this data, exposure to this risk factor has decreased in time. Male drivers, not using seatbelt correctly carried passengers in the cargo area more frequently. Results support the importance of improving and enforcing current legislation and evaluating strategies directed to prevent exposure to this risky behavior with the potential of contributing to lowering the high burden that road traffic injuries imposed in Mexican public health.