Parvalbumin (PV)-positive basket cells mediate fast cortical perisomatic inhibition. We studied development and mechanisms of long-lasting synaptic plasticity at excitatory synapses in fast spiking, PV-positive basket cells. Whole-cell patch-clamp recordings were obtained from layer 2/3 basket cells in motor cortex slices (BL6 mice, P13–63, 34°C). Extracellular stimulation evoked monophasic EPSCs with short latency in the recorded basket cells. An associative high frequency induction protocol reliably induced long-term potentiation (LTP, 176 ± 16 % of baseline, 30–120 min, n=12) in adult basket cells (>4 weeks old). In young basket cells (2–3 weeks old), LTP was absent (101 ± 8 % of control, n=13), indicating a late developmental onset of LTP. Induction of LTP required a postsynaptic calcium increase, as 30 mM BAPTA blocked LTP (101 ± 9 % of control, n=8), but was NMDA-receptor independent, as LTP persisted (181 ± 10% of control) in APV (50 microM, n=8). However, the mGluR5-receptor antagonist MPEP (1 microM, n=7) blocked LTP (104 ± 12 % of control), indicating a novel role of mGluR5 in cortical plasticity. We have identified a novel mechanism of adult cortical plasticity, which may play a role in mGluR5-related brain disorders such as addiction and schizophrenia.