The aim of the study was to design an accurate and useful observational instrument for evaluating basic turn techniques in alpine skiing, and to determine its validity and reliability. A multi-step approach was used to design and validate the instrument: a literature revision; an expert meeting; a pilot test; the assessment of intra- and inter-observer reliability; a convergent validity test; and the responsiveness calculation with a pre- post-test. Results showed adequate values of intra-rater (P=0.80-0.83) and inter-rater reliability (P=0.86-0.97). For the convergent validity, a moderate statistically significant correlation for the speed and trajectory control dimensions were achieved (rho=0.58-0.65, p<0.001), but not for the balance position dimension (rho=0.24, p=0.166). The responsiveness was also acceptable (p<0.05, r=0.46-0.60). In conclusion, the Alpine Ski Technique Observation Instrument is a useful, reliable, valid, and responsive observational tool.