Midbrain dopaminergic (mDA) neurons control movement and emotion, and their degeneration leads to motor and cognitive defects in Parkinson's disease (PD). miR-133b is a conserved microRNA that is thought to regulate mDA neuron differentiation by targeting Pitx3, a transcription factor required for appropriate development of mDA substantia nigra neurons. Moreover, miR-133b has been found to be depleted in the midbrain of PD patients. However, the function of miR-133b in the intact midbrain has not been determined. Here we show that miR-133b null mice have normal numbers of mDA neurons during development and aging. Dopamine levels are unchanged in the striatum, while expression of dopaminergic genes, including Pitx3, is also unaffected. Finally, motor coordination and both spontaneous and psychostimulant-induced locomotion are unaltered in miR-133b null mice, suggesting that miR-133b does not play a significant role in mDA neuron development and maintenance in vivo.