This work provides the first linguistic description of Isaalo (Western Sisaala SSL]), a language spoken by less than 10,000 people in and around Lambussie, in the Upper West Region of Ghana. It presents a detailed phonological description and includes an orthography proposal for this previously unwritten language. Included is also an overview of Isaalo morphology, a 1200 word lexicon and a transcribed interlinear glossed text. This work establishes Isaalo as a distinct language within the Sisaala language complex and disambiguates it from closely related Sisaala languages spoken in Northern Ghana and Southwestern Burkina Faso.