All-male boards have surged by 73% across AIM-listed companies this year, according to a recent analysis by WB Directors.
While FTSE 100 companies have eliminated all-male boards, smaller firms are moving in the opposite direction.
Some 190 AIM companies now have no women on their boards, up from 108 in 2023.
It means 35% of all companies on the junior market are run by all-male boards, a significant increase from 18% last year.
The shift is partly due to a mix of female directors being replaced by men and the listing of previously private companies with all-male boards.
AIM companies often have more founding family members and representatives from private equity, a male-dominated sector, which contributes to the lack of gender diversity.
Fiona Hathorn, chief executive of WB, said: “I sense a real danger of attention drifting on this issue.”
She pointed out that the growth of the “anti-ED&I agenda” is “deeply unhelpful” and might be influencing company decisions.
Additionally, the data showed that women in AIM companies hold only 6.6% of key roles such as chair, chief executive, finance director, or senior independent director, compared to 24% in FTSE 100 companies.
Some AIM companies justify their male-only boards by citing the need for expertise in areas where women are traditionally underrepresented, such as IT.
They also mention the importance of keeping boards small and cost-effective.