To evaluate transcranial magnetic stimulation (TMS) measures of inhibition and excitation in obsessive-compulsive disorder (OCD), major depressive disorder (MDD) and schizophrenia (SCZ). Methods: Paradigms included: short-interval cortical inhibition (SICI), cortical silent period (CSP), resting motor threshold, intracortical facilitation, and motor evoked potential amplitude. A literature search was performed using PubMed, Ovid Medline, Embase Psychiatry and PsycINFO 1990 through April 2012. Results: A significant Hedge s g was found for decreased SICI (g= 0.572, 95 confidence interval [0.179, 0.966], p= 0.004), enhanced intracortical facilitation (g= 0.446, 95 confidence interval [0.042, 0.849], p= 0.030) and decreased CSP (g= -0.466, 95 confidence interval [-0.881, -0.052], p= 0.027) within the OCD population. For MDD, significant effect sizes were demonstrated for decreased SICI (g = 0.641, 95 confidence interval [0.384, 0.898], p= 0.000) and shortened CSP (g= -1.232, 95 confidence interval [-1.530, -0.933], p= 0.000). In SCZ, a significant Hedge s g was shown for decreased SICI (g= 0.476, 95 confidence interval [0.331, 0.620], p= 0.000). Conclusion: Inhibitory deficits are a ubiquitous finding across OCD, MDD, SCZ and enhancement of intracortical facilitation is specific to OCD. Significance: Provides a clear platform from which diagnostic procedures can be developed. ? 2013 International Federation of Clinical Neurophysiology.