In that year, they joined the Extraliga, after winning a promotion-relegation play-off against HC Slovan Ústečtí Lvi.

In each of its first three seasons in the Czech Extraliga, Mladá Boleslav had to win a best-of-seven promotion-relegation play-off to stay in the top league, beating Slovan Ústečtí Lvi 4–3 in the last of them.

In September 2011, locally born Radim Vrbata of the NHL's Vancouver Canucks, bought a 33% share in the club, which he held until 2015.

In April 2012 the club finished in last place and lost the subsequent promotion-relegation play-off against Piráti Chomutov in seven games.

After this game BK Mladá Boleslav's management submitted an official protest to the league's governing body over a number of controversial umpiring decisions during the match, but the league commission rejected all three appeals, and Piráti Chomutov and Bílí Tigři Liberec therefore remained in the Extraliga for the 2013/14 season, and BK Mladá Boleslav and HC Olomouc remained in the První Liga.

In the first round of the play-offs they defeated local rivals Benátky nad Jizerou 4–2 in a best-of-seven series ending on March 3, 2014.

They defeated their semi-final opponent HC Horácká Slavia Třebíč by 4–0, qualifying for the play-offs for a second year in a row.

On 18 April 2014, despite losing to Olomouc 5–4 in overtime, Mladá Boleslav won their return to the Extraliga for the 2014/15 season after a two-year absence.