This paper presents an experimental research work to determine temperature gradients in concrete bridge girders under natural environmental conditions. Three AASHTO Type I-girders having different configurations (with and without wide top flanges) were considered in the experimental program. Temperature was monitored in the bridge girders to determine the vertical and transverse temperature gradients in a predeck placement condition. It was found that uneven heating of optimized bridge girder sections results in large nonlinear temperature gradients. The current AASHTO design standard, which only uses a nonlinear vertical but no transversal temperature gradient, was found inaccurate to predict both shape and magnitude of temperature gradients for the analyzed girders.