A comparative study was conducted to highlight key differences in the required amounts of prestressing and passive reinforcement for externally and internally prestressed box-girder bridges. The reinforcement is designed on the basis of combined serviceability and structural safety criteria for varying span length and girder slenderness. Under the assumptions of the study, the externally prestressed box-girder is shown to require up to 25 % more prestressing force for girder heights around 2 m. At girder heights above 3.5 m however, internal prestressing becomes the more favorable type of prestressing. The study also shows that the externally prestressed girder tends to require more longitudinal and shear passive reinforcement in key design sections.