Parablennius ruber, the red or Portuguese blenny, is reported from the British Isles. This species has recently been revalidated as separate from P. gattorugine and this, together with confusion about the field identification characteristics which distinguish the two species, is likely to have resulted in it being under-recorded. Parablennius ruber was found to be fairly widespread on the exposed west coasts of the Republic of Ireland and Scotland (22 records), with additional records from the Isles of Scilly (3 records) and Northern Ireland (1 record). One record was made of egg guarding. Most records were from exposed areas of bedrock and boulders, between 15 and 30 m in depth. Field identification characteristics which distinguish between P. ruber and P. gattorugine are given. Given that its original description was from Ushant in 1836, it is unlikely that P. ruber is a fairly recent addition to the British fauna as a result of increased water temperatures. However, given its habitat, the fairly recent advent of sampling by SCUBA diving is likely to have increased the potential for sightings. The growth of SCUBA diving and the increase in the use of underwater digital photography are likely to result in a better knowledge of its distribution.