Neuropsychological diagnostic tests of visual perception mostly assess high-level processes like object recognition. Object recognition, however, relies on distinct mid-level processes of perceptual organization that are only implicitly tested in classical tests. The Leuven Perceptual Organization Screening Test (L-POST) fills a gap with respect to clinically oriented tests of mid-level visual function. In 15 online subtests, a range of mid-level processes are covered, such as figure-ground segmentation, local and global processing, and shape perception. We also test the sensitivity to a wide variety of perceptual grouping cues, like common fate, collinearity, proximity, and closure. To reduce cognitive load, a matching-to-sample task is used for all subtests. Our online test can be administered in 20-45 min and is freely available at www.gestaltrevision.be/tests . The online implementation enables us to offer a separate interface for researchers and clinicians to have immediate access to the raw and summary results for each patient and to keep a record of their patient's entire data. Also, each patient's results can be flexibly compared with a range of age-matched norm samples. In conclusion, the L-POST is a valuable screening test for perceptual organization. The test allows clinicians to screen for deficits in visual perception and enables researchers to get a broader overview of mid-level visual processes that are preserved or disrupted in a given patient.