Just over 46,000 vehicles were registered north of the border - a year-on-year increase of more than 2.7%.
However, UK sales increased by 5.3% to almost 519,000 - the strongest month recorded since 1999.
March is typically the biggest month, accounting for about a fifth of the year's car registrations.
Last month saw Vauxhall retain its position as market leader in Scotland, with more than 10,000 units sold.
The Vauxhall Corsa remained the most popular new car, while the Ford Fiesta had a strong month and moved into the number two spot for the year to date.
The figures were compiled by the Society of Motor Manufacturers and Traders.
Top Scottish sellers in March
1. Vauxhall Corsa 2,575
2. Ford Fiesta  1,772
3. Vauxhall Astra 1,249
4. Ford Focus 1,126
5. Volkswagen Polo 1,077
Source: SMMT
Scottish Motor Trade Association chief executive Sandy Burgess said: "All areas have experienced growth with the exception of Dumfries and Galloway and Strathclyde.
"The reductions however are minimal and with the fantastic growth on 2015 numbers elsewhere, we have come out of this critical sales period well ahead for the year to date.
"We have been aware of some dealers who were experiencing new vehicle delivery issues towards the end of the month, and this may well have had a small but noticeable negative effect.
"The rest of the UK continues to show stronger growth but as we have mentioned previously this may not all be down to sales with specific manufacturers and dealers taking tactical decisions on registrations."
New car sales in Scotland grew last month but at half the rate of the UK as a whole, according to motor traders.