Laser powder bed fusion has seen an increase in use due to its ability to build components with fine features that cannot be made using other more traditional manufacturing methods. However, these precise features are challenging to qualify during printing due to their sensitivity to thermal and mechanical instabilities as they approach machine and process limits. While in situ measurements may allow for parts to be qualified before printing is completed, the small scale of features increases the difficulty of detection for geometric and quality defects. In this work, thin vertical walls with slits, rectangular and unsupported gaps in the wall, were printed and measured for their dimensional accuracy via layer wise in situ optical images. The wall thickness, manufacturing energy density, and slit orientation were varied to investigate the impact of both geometric design and manufacturing parameters. The walls were then measured using high resolution ex situ X-ray computed tomography scans to measure the dimensional acc[VH1][BJ2]uracy of the thickness and slits. These scans also served as a ground-truth verification for the validation of the measurements from the in situ optical images. The resulting walls showed that the slits were the parameter that had the largest impact on dimensional accuracy. Slits with a higher horizontal aspect ratio (defined as a slit with a larger width than height) had dimensional inaccuracy dominated primarily by dross formation, while slits with a lower horizontal aspect ratio had dimensional accuracy dominated by contact with the recoater blade. These trends were amplified by wall thickness, as thinner walls were more susceptible to geometric errors. Meanwhile, energy density had a more complex impact, higher energy densities led to more solid walls less impacted by horizontal shifting due to contact with the recoater blade but also increased dross on the underside of the slits. Optical imaging revealed localized spatter in overhang layers consistent with prior process observations. Multiple image processing techniques were employed to perform in-situ dimensional validation; popular techniques such as active contours were found to be increasingly inaccurate as the designed part’s thickness decreased.[VH3][VH4] While layer wise images may inform structural trends, the role of future layer interactions was found to account for many apparent deviations between the optical monitoring and final X-ray computed tomography scan. This work provides a deeper understanding of necessary factors for designing, manufacturing, and qualifying thin-walled, slitted parts for a variety of applications including heat exchangers, cooling plates, and fan blades.