Abstract A description is provided for Cercospora citrullina [Didymella bryoniae] . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS. Cucurbitaceae: Benincasa, Blastania, Bryonia, Citrulus (water melon), Coccinia, Clocynthis, Cucumis (melon, cucumber), Cucurbita (pumpkin), Lagenaria, Luffa, Melothria, Momordica, Sechium, Telfairia, Trichosanthes . DISEASE: Leaf spot of Cucurbitaceae . On the water melon the leaf spots occur first on the younger leaves. The small grey or white spots, bordered by a black margin, gradually increase in number and spread over the leaf surface. On cucumber, musk melon and squash the leaf spots are larger, 0.5-10 mm diam., and grey-ochre. The centre of the lesions eventually becomes transparent and brittle. The disease may cause leaf fall. GEOGRAPHICAL DISTRIBUTION: Most tropical and subtropical countries. Africa: most countries; Asia: most countries; Australasia and Oceania: Central Pacific, Fiji, Papua New Guinea, Solomon Islands, South America: Bolivia, Brazil, Venezuela. TRANSMISSION: Disseminated by wind-borne conidia, contaminated tools, and rain splashes. The fungus apparently over seasons in crop debris, and on weeds of the Cucurbitaceae (Chupp & Sherf, 1960).