Microscopy offers an indispensable technique for visualizing biological processes and for defining cytological abnormalities characteristic of disease. However, combining microscopy with the power of pooled CRISPR screening presents considerable technical challenges, hindering application of systematic genetic analysis to imaging-defined phenotypes. Here, we establish a fluorescence microscopy-based CRISPR screening platform that combines ease of implementation with flexible analysis of live-cell or antibody-based molecular markers, including post-translational modifications. Applying this methodology, we systematically identify regulators of primary cilium structure and function in human cells through targeted and genome-wide screens. We further show that integration of screens focused on distinct ciliary phenotypes yields multi-dimensional profiles that delineate precise gene functions. Among the identified hits, TZMP1 (SMIM27) encodes a microprotein at the ciliary transition zone that is required for ciliogenesis in human cells and for ciliary function in Xenopus embryos. More broadly, our approach provides a technological and conceptual strategy for microscopy-based functional genomics.