Leaves with yellow midribs are routinely observed in sugarcane plantations in Thailand and the question was, whether Western X-disease phytoplasma was also prevalent in Thailand causing this symptom, in addition to the infection by Sugarcane yellow leaf virus (Lehrer et al. 2008). Already known is Sugarcane white leaf phytoplasma in Southeastern Asia, India and Taiwan (Wongkaew et al. 1997; Chen and Kusalwong 2000). It is easily recognized by the emerging white leaves at the top of the infected plant or from white Northeast Thailand and considered to be “now under control in infected areas” (Chen and Kusalwong 2000). Sometimes yellow leaves stay next to the white leaves on a stalk, which gives the impression that leaf yellowing may be an early stage of the white leaf symptom. We wanted to know if the leaves with yellow midribs in the Thailand sugarcane plantations really contain aWestern X-type phytoplasma, which is responsible for Leaf Yellows in Africa and Cuba (Arocha et al. 1999; Cronje et al. 1998), or whether it is a “mild” symptom of the White leaf phytoplasma infection. We collected leaves with yellow-midrib and green leaves from sugarcane plants from Khon Kaen (Northeast province), from Suphanburi (Central Thailand) and Bang Phra (Chonburi province, Southeast Thailand) to find out if Leaf yellows phytoplasma or White leaf phytoplasma is responsible for the yellowing symptoms.