Reexamination of some previous collections of marine algae from the Northwest Hawaiian Islands (NWHI), also known as the Leeward Hawaiian Islands, and the addition of more recent collections have resulted in recognition of 48 taxa of Chlorophyta (green algae), with eight new records for the NWHI; 33 taxa of Phaeophyta (brown algae), with seven new records; and 124 species of Rhodophyta (red algae), of which 26 are new records for the NWHI. Among the 41 new records, 14 taxa are newly reported for the entire Hawaiian archipelago. Among the new records are Nemacystus decipiens, Halimeda copiosa, and H. velasquezii and among the microscopic algae Crouania mageshimensis. Total macroscopic marine flora consists of 205 taxa, a number close to the 222 species known from Eniwetak in the northern Marshall Islands. Proportions of greens and reds in the two places are markedly different, however, with more green and fewer red species in Eniwetak.