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Crystals of semicarbazide hydrochloride, NH2CONHNH+3Cl– are paraelectric above 294 K and ferroelectric below. The Raman spectra in the region 0–1800 cm–1 of oriented single crystals of semicarbazide hydrochloride and its perdeutero analogue have been recorded over the temperature range 298–87 K. In addition the infrared spectrum of semicarbazide hydrochloride in a KBr disc at 298 K has been recorded in the range 250–1700 cm–1. The Raman spectra have been analysed in relation to the structural changes occurring with the change of phase. The spectroscopic results support the X-ray evidence that the transition to the ferroelectric phase is second order and involves no major structural change. Comparison of the infrared and Raman spectra suggest that LO–TO splitting is unimportant.