Understanding the physiological function of the intrinsically disordered microtubule associated protein (MAP) Tau has proven challenging. Tau, primarily expressed in neurons, is known to have a variety of axonal functions, including regulation of microtubule dynamics and modulation of kinesin motor motility. Interestingly, research on the microtubule binding behavior of Tau reveals that Tau binds to the microtubule surface in a dynamic equilibrium between static and diffusive states. Although it is understood that the binding state equilibrium plays a role in physiological Tau function, such as modulation of kinesin motility, it is less understood how disease associated mutations affect Tau binding behavior and function. The canonical theory states that mutations in Tau reduce Tau affinity for the microtubule. Here, we investigate the role of an N-terminal disease associated mutation in Tau, R5L, using an in vitro reconstituted system for single molecule Total Internal Reflection Fluorescence (smTIRF) Microscopy. Contrary to the canonical theory, we determined the R5L mutation does not reduce Tau affinity for the microtubule. Rather, the R5L mutation reduces the total amount of Tau bound to the microtubule at saturating conditions. Our data suggests the R5L mutation reduces Tau:Tau interactions, decreasing the ability of R5L-Tau to form larger order complexes, known as “Tau condensates.” Currently, we are determining the mechanism by which this occurs, potentially due to a structural change associated with the R5L mutation. Altogether, these results challenge the current paradigm of how mutations in Tau lead to disease.