The Renault group increased its share of the French passenger car market 0.7 points year on year for a 23.2% share but the automaker's regional chief branded results "unsatisfactory".
The group took a 21.8% share (-2.3 points) of the car and light commercial vehicle (LCV) market, which continued to fall (-10.5%).
The new Clio was the top-selling vehicle in France for the first five months of the year.
Dacia's Sandero was the best-selling retail sales vehicle in May.
In a market off 10.3%, the group registered 30,837 vehicles in May (-16.5%), for a 20.8% share, down 1.5 points on 2012.
The Renault brand registered 24,005 vehicles in May, for a market share of 16.2% (-2 points).
The automaker blamed "temporary manufacturing constraints linked to the launch of Captur in Europe and the success" of new Clio and Sandero models plus a policy "to considerably reduce registrations with short-term leasing companies, which are low on profitability" (-2,800 units).
With 7,317 registrations in May and 44,456 for the year to date, the Clio remained the top seller in France at the end of May.
French Captur registrations reached 2,660 in May.
With 2,830 registrations to the end of May, the Zoe, the best-selling electric vehicle in France, accounted for 73% of the electric car market.
Dacia registered 6,832 vehicles in May, growing its market share 0.5 points and ranking fifth largest brand for the year to 31 May.
In a market down 11.2%, the group registered 7,656 vehicles in May (-27.8%), for a 27.1% share of the market.
The Kangoo remained the best-selling LCV in France YTD, with 12,824 registrations.
With 1,730 registrations the Kangoo ZE accounted for 83.6% of the electric LCV market YTD.
Renault's French region chief Bernard Cambier said: "Our performance in May was not satisfactory. But it does not reflect the reality of our sales activity, as orders remain strong and our order book is up on last year.
"The launch of Captur in Europe and the success of new Clio and Sandero are generating temporary manufacturing constraints. The shortfall will soon be overcome, enabling us to bring registrations back into line with our commercial performance on orders."