<p>Over the past two decades, the growing demand for housing in Latin America has led to the widespread use of thin reinforced concrete wall buildings (TRCWB) in construction projects. These buildings, particularly those of low to medium height, typically feature wall thicknesses between 80 and 150 mm, reinforced with single or double layers of electro-welded wire mesh (WWM), and sometimes include boundary elements. Both experimental and numerical studies have highlighted limitations of this structural system, including a low capacity for inelastic deformation due to the use of WWM as web reinforcement, and sudden failures caused by concrete crushing and reinforcement buckling concentrated at the wall edges. However, the slab impact on the seismic performance of the system has not been extensively assessed through numerical modeling or experimental analysis, and numerical studies typically use two-dimensional models that do not explicitly consider slabs. This study evaluates the impact of slabs on the seismic performance of low- and mid-rise TRCWB. An analysis of two buildings in Colombia, representing low-rise (5-story) and mid-rise (15-story) structures, was conducted using OpenseesPy. In three scenarios, MVLEM-3D elements were used for walls and shell-type elements for slabs: no slabs, linear slabs, and non-linear slabs. Nonlinear static and response history analyses were employed to assess the seismic response, revealing that models excluding slabs tend to overestimate deformation capacity and underestimate shear capacity by factors between 1.1 and 2.0. The absence of slabs also predicts higher fragility values, especially under severe damage conditions. Interestingly, models with linear slabs produced results similar to those with non-linear slabs, indicating that non-linear behavior is primarily concentrated in the walls. This highlights the importance of including slabs for an accurate assessment of the seismic performance of TRCWB.</p>