A diesel exhaust treatment device comprising: a main body having a central longitudinal axis that extends between first and second ends of the main body; a catalyzed substrate positioned within an interior of the main body, the substrate having an upstream face; and a side inlet positioned at a side of the main body for directing exhaust gas into the interior of the main body; wherein a flow distribution element is positioned within the interior of the main body at a location between the side inlet and the upstream face of the substrate, said device being characterized by the flow distribution element extending across a direction of exhaust flow through the main body, the flow distribution element being positioned at a portion of the main body that is opposite the side inlet, the flow distribution element including a first edge that contacts the main body and a second edge that traverses an interior region of the main body, the flow distribution element having a central portion defining a first dimension measured along a reference plane that bisects the main body along a length of the main body and the side inlet, the first dimension being less than 50 percent of a cross-dimension of the main body measured along the reference plane, the first dimension being measured from the second edge to the first edge, the flow distribution element also including side portions (23, 25) that define second dimensions that are larger than the first dimension, the second dimensions being measured in an orientation parallel to the reference plane, the second dimensions being measured from a reference line tangent to a location wherein the first edge intersects the reference plane to the second edge. a main body having a central longitudinal axis that extends between first and second ends of the main body; a catalyzed substrate positioned within an interior of the main body, the substrate having an upstream face; and a side inlet positioned at a side of the main body for directing exhaust gas into the interior of the main body; wherein a flow distribution element is positioned within the interior of the main body at a location between the side inlet and the upstream face of the substrate, said device being characterized by the flow distribution element extending across a direction of exhaust flow through the main body, the flow distribution element being positioned at a portion of the main body that is opposite the side inlet, the flow distribution element including a first edge that contacts the main body and a second edge that traverses an interior region of the main body, the flow distribution element having a central portion defining a first dimension measured along a reference plane that bisects the main body along a length of the main body and the side inlet, the first dimension being less than 50 percent of a cross-dimension of the main body measured along the reference plane, the first dimension being measured from the second edge to the first edge, the flow distribution element also including side portions (23, 25) that define second dimensions that are larger than the first dimension, the second dimensions being measured in an orientation parallel to the reference plane, the second dimensions being measured from a reference line tangent to a location wherein the first edge intersects the reference plane to the second edge.