Llanidan is a parish in south-west Anglesey, Wales which includes the village of Brynsiencyn. The parish is along the Menai Strait, about 4 miles north-east of Caernarfon (across the strait). The parish church of St Nidans is near the A4080 highway, a little to the east of Brynsiencyn. The ruins of an earlier parish church survive.